I think a perfect example of how it is possible to teach oneself using a variety of texts is found in looking at western (weapons based) martial arts. In the last 20 years or so these have seen a revival, going from being thought essentially non-existant to being very complete systems of armed combat. These people taught themselves mostly by looking at centuries old manuscripts and 'figuring it out' over years. There are a lot of very high quality swordsmen (and axemen/spearmen, whatever) that have learned in this manner, easily as good as their more formally trained japanese/chinese style counterparts. The historical fencing guys for example are extremely good, then there's various organisations like dagohir groups, things like ARMA and the SCA. These groups all include a lot of people who have a lot of skill, yet many of these people were either self taught or taught by someone who was self taught. Its a matter of time and effort, people dedicated their lives to reviving WMA and as far as I can see they've been quite sucessful. Also note, this is an outsiders observations... I like to collect swords and do a little backyard cutting, which is mostly how I got my exposure to WMA, but I'm no swordsman and no member of any WMA group.

I'm gonna play devil's advocate on this one...when I watch videos of ARMA and other WMA, they are often very impressive.

However there's no question in my mind that a lot of the original adherents of WMA revival idea had some training in Judo, Karate, Greco-roman wrestling, Ju Jutsu.. what have you.

You can't learn to throw ogoshi from some old manuscripts alone, so while a large part of the curriculum might come from reconstructed sources, it's pretty clear that the fact that ARMA etc. people already had some martial experience plays a big role in the WMA community.