The fact is they did leave information. The names of each of the Forsaken was known to the wider populace, the name Lewis Therin was well known to the wider populace. The story of the Dragon and the breaking of the world and the magic of the ages. Even tales from the first age are known, stories of flights to the moon, war between the USSR and Nato etc these tales are all told as fables and stories.
Now why didn't they leave a detailed how to manual for the destruction of each of the forsaken, sealing of the bore and the weakness and abilities of the minions of the Dark lord? Instruction on weaves, technology and a manual for the use of all those tools.
The fact is they might have done.
the remaining female Aes Sedai in Paaran Disen bound the Da'shain Aiel to an oath to protect an’greal, sa'angreal, and ter'angreal and other objects from the madness of the male Aes Sedai. The Da'shain Aiel are commanded to "keep moving, always moving until they find a place of safety", where none can harm them.
That collection may well have contained artefacts loaded with knowledge, the ages version of a USB stick, or a Hard drive with an idiots guide to destroying the dark lord. It certainly contained weapons but it also contained other items that have long lost all knowledge of use.
And that is the biggest issue. You ask why is there not a repository, that single collection was travelling for generations. the group carrying it split into 3 groups, 2 of which became the Aiel as we know them in the books and then Tinkers, long forgetting their own history.
Imagine the destruction of the world, Robert Jordan wrote that the war of shadow destroyed all industrialisation across the entire world and killed millions. Imagine that in our own world, every industrial centre wiped out and the population reduced to trying to survive.
Then add in the Breaking, 100 years of all male channellers in existence destroying the world. This is not nuclear Armageddon, it is much much worse. Balefire changing time, entire cities eradicated in a few minutes. The actions of individuals undone. Again Robert Jordan explains that entire continents where destroyed and new landmasses raised. Picture the scenes of the movie 2020. And I will say again Balefire, a weave that literally burns away the impact someone or something has had on the pattern. We know in the breaking at least 1 city is fully burnt away with Balefire, that power of balefire would potentially undo anything done in that city maybe years prior (the details of how balefire works are wooly at best).
Now this breaking was not planned for, not forseen, it happened suddenly and caught the female Aes Sedai by surprise. The moment the breaking happened any sa'angreal, and ter'angreal that required the male half became useless and possibly dangerous to use. So if that USB stick was created by a male channeller it was lost.
Now let's picture the scene post this. You ask why where there are not manuals, records, writings, where would they have been kept safe? Paper would have been destroyed, lost, or over time those keeping it would have lost sense of the context.
When the White Tower is founded it is created by female channellers who claim to be Aes Sedai and, some knowledge is known, female channellers did not learn from scratch, they had weaves and an understanding of saidin and sadir, they had an understanding of what had happened in the war of shadow and the breaking. But, that knowledge has, over 3500 years, been slowly lost and forgotten largely because Humanity as a whole had more important things to worry about. Survival, losing a huge % of the population (Robert Jordan said humanity almost became extinct), trying to make the wasteland that remained of the world habitable while fighting the remains of the dark lords armies.
You also then had the civil wars, the re establishment of civilisation, in the words of Galadrial History became legend. Legend became myth and much that should not have been forgotten was lost.
There is a moment in the book where one of the Forsaken is in the White Tower, in one of the rooms where Ter'angreal who's purpose is not known are stored. She looks at the items and smiles at the stupidity of the Aes Sedai, I am pretty sure Robert Jordan describes one item being like a TV, another like a Mobile Phone, all powered by the one power and, probably not working because there is no Mobile Phone Coverage or TV stations to pick up. She remembers other mundane items who's creation has been lost, even she did not know how to make them.
That one scene over a few pages demonstrates again how wide and complete the breaking was.
But there are also bits of information. One of Rands actions is to create the School of Cairhien, he does this in part to ensure that if he does break the world again then the knowledge regained in this time is not lost. Historians, Philosophisers, Scientists etc all come to learn, teach and share knowledge. He sets up a library, again to try and undo the records lost during the breaking,
Herid Fel manages to gather enough records to have a breakthrough as to how to seal the bore and darkone away in such a way that he can be "re found" again in the future long after the events of all of this are forgotten. (remember all that has been will happen again and the dark one has been found, released and sealed away many times).
The Aes Sedai also have records, and there are other records all over the world. There are also Ter'angreal, stored in private collections, Bayle Doman has a few for instance, the Seanchan have many more.
Again who knows if one or many of these are not record stores, details of the war and a detailed how to, but, the purpose or use has been long lost. Aes Sedai can't figure out how to operate them.
The Doorways the Aes Sedai use to test novices might actually be a way f accessing this history, but they have forgotten.
Or the items you speak of might lie, buried under the ground, waiting to be dug up, discovered or for nature to reveal them.
So the answer to your question is that no, the issue was not just poor record keeping. It was the fact that the Breaking was un planned and could not be prepared for, the 3500 years where civilisation was sent back to the middle ages could not be planned or prepared for. But, in fact, a lot of information was known and recorded as seen throughout the books through what Rand manages to gather together and, Rhuidean, remember that city is full of items and the Aes Sedai have not yet figured out what any of it is actually capable of or contains. It might be that post the last battle they find the complete and total history of the age of Legends and a manual explaining what every single item found does.
In the Dragon Reborn Verin shows this loss of knowledge over time to Egwene.
Fascinating this. Rosel of Essam claimed more then 100 pages survived the Breaking, and she should have known since she wrote barely 200 years afterwards, but only this one piece still exists, so far as I know, maybe only this very copy. Rosel wrote it contained secrets the world could not face, and she would not speak of them plainly, I have read this page a thousand times trying to decipher what she meant.
The page is in a language that requires translating, and Verin proceeds to recite it, but, this single passage shows that written documents expected to survive the breaking, the world, and more over 3000 years of rebuilding human society the best you can expect to survive are scraps, some in languages long lost so reliant on poor translations.
Later in the same book Morraine, on learning that Be'Lal is in Tear, asks Loial what the Ogier remember of him. When Faile gets angry at her lack of knowledge and asks why she asks the Ogier Morraine explains that it has been over 100 generations since the Breaking for Humans but less then 30 for Ogier and there stories still contain information that Humans long ago lost.
So that is at least 2 places in book 3 of the series that Robert Jordan indicates the amount of knowledge that was lost since the breaking. Your idea that "record keeping" could have been better, you can't plan for 3500 years of history, or nations being destroyed, rebuilt and destroyed again and of entire continents being ripped apart.
