A bunch of us BW guys had a discussion about this and that is the conclusion I came to. Here's the discussion:
From what I can tell the "snorkel" type parka was used all the way up until Flecktarn. However, the special issue 1970s GJ two piece jacket (shell and nylon liner) became the type you have sometime in 1986 and that became the basis for the Flecktarn parka used in trials and then eventually in full production.
That thread reminds me that I did locate pretty much everything since then and so I should take some pictures and update the thread.