Some later printings add works missed in earlier printings, etc. The Taisho Tripitaka, for example, includes an appendix of such material. There is no religious committee deciding what to include. It is an editorial decision only. No Church councils are, however, involved in the decision.
Laymen generally support such publication since it is a meritorious act.
In fact, having a Buddhist book printed is a meritorious act even if you can't read. One work illustrating both possibilities is the Svarnaprabhasottama or Gold Gleam Sutra. Not only were there several texts floating around but one of the Tibetan versions was from a Chinese version and not from the Sanskrit. Bit like the Bible vs. the Old Testament. Yes there were Buddhist congresses that put together collections of text, the monastic law in particular but nothing like the decisions that led to our Bible.