Were any of his languages developed enough that he could just write or even talk with them without using any kind of dictionary, wordlist, or grammar helper? In other words, did he actually know them?
I don't believe there is any way to truly know, but personally I believe that he knew every word he ever made by heart. This is due to the fact that in every instance where a made up word is used, it is applied to the story in a very specific manner, like songs, greetings, or names which have meaning (Gandalf - Gand Alf - Wand Elf). Also, the fact that he worked on Lord Of The Rings for 17 years, makes me believe that he got pretty familiar with his languages. (Not to mention that Tolkien developed some of the languages before even the Hobbit!)
It is often cited that Tolkien developed his languages mainly with the thoughts of creating names for his characters and locations, and even small phrases. He admitted in a letter himself (sorry but I don't have the citation available right now) that he didn't develop their grammar and vocabulary as much as to make compositions or talk with them.
Common logic says that since he worked on them for many decades, of course he had already memorized many elements and could easily invoke them from his mind, especially the most common ones, and create new words and names on the fly.
However common logic also says that it's impossible to remember all that corpus, and indeed Tolkien made notes which he consulted while writing so that he could keep a consistency with his previous ideas. Such a work is the document "Etymologies", a set of his personal etymological notes which he started in the 1930s and still revised and consulted it while writing LOTR. The document as published in the fith volume of the History of Middle-earth.