I did not check on the details, but I remember that the whole point of carbon freezing Han Solo is to test the carbon freezing technique - which is claimed to have never been done on a living organism - to make sure Luke Skywalker can be frozen and brought to Palpatine intact and unharmed.

But this clip from the Clone Wars show that it has been done before, and it is possible that such a technique, while probably not recommended, is not unheard of. So why did they say that Han is the first, in-universe?