The written "classics" of taiji, xingyi and bagua in all probability date only to the mid- to late-1800s. The oral teaching formulae (or "songs") of taiji and xingyi may be a little older, but how much older is speculative. Chang Naizhou's book, the first book (that I'm aware of) in any language that details specifically internal principles of martial practice, is as you note from the 1700s (for those interested, a capsule summary of Chang's life and a good translation of a short excerpt by Jarek Szymanski can be found at http://www.chinafrominside.com/ma/ot...s/CNZbook.html
). Qi Jiguang's book is from the late 1500s and is Shaolin-based. Sun Tzu's The Art of War
is, however, substantially older, and antedates the Shaolin Temple by almost a thousand years (and so would not be Shaolin-based),
The Mawangdui pictures of Tao-yin (Oh, wait... does that have something to do with the "Tao" aka "Do"?) exercises comes from BCE, making these types of body-skill practices at least that old and probably a lot older. "Shaolin" and "Neijia" have little to do with it.
Zhang Naijou's comments about practicing these skills is only a remaining commentary of and extremely wide and ancient corpus. The fact that much literature has been lost to book-burnings, history-revisions, and so on, has little to do with it... as the Mawangdui materials show.
However, little by little the provincial views of "it's a specialty of Japan" has evolved into "it's a relatively recent development in China" and will soon be "hey, this stuff is far bigger and older than we thought" and gradually will grow into an understanding of why the characteristics of Buddha's body were considered 'special'... yet a part of this whole story. Provincialism withers in the light of history and science.