Very nice condition! These items were generally worn out and destroyed as the cloth is very thin. Often I've seen them in generally good condition, but the knees are nearly "white" from wear. Rips and repairs are often found.
The red thread is associated with samples for evaluation. Sometimes it is for a brand new design, sometimes it seems it's for quality control purposes for new production of an existing design. I say this because I have examples of both unique and standard items with red thread.
Belgian camouflage is a fun thing to collect. There are tons of things to collect. I think I started a thread about the various different types, but I can't find it. All I found was the ripstop variants:https://iacmc.forumotion.com/t12369-belgian-jigsaw-ripstop-variants
I found some notes for Jigsaw trousers:
1. 3 pocket canvas (1958 and a few in the early 1960s)
2. 8 pocket in either poplin or lightweight cotton (1967 through 1970s)
3. 6 pocket poplin (late 1970s through 1980s)
4. 5 pocket cotton (limited early 1990s issue)
5. 6 pocket in two different types of ripstop and one type of heavy cotton (1997-2012?)
And some notes on the various smocks/jackets in Moon & Balls and Brush Stroke patterns:
M&B Smocks/Trousers -> 1952-1955
Brush Smocks/Trousers -> 1954-1955
M&B/Brush Jackets (Snaps)/Trousers -> 1956
M&B/Brush Jackets (Buttons)/Trousers -> 1956
Brush Smock -> 1975 (not sure if there are other years)
Brush 8 pocket poplin trousers -> don't know date, but probably 1970s
At some point I should document everything I know of in one place.