Yes, I would say any prime condition Buck knife is collectible.
(reposted information, 'search' is your friend) Kraton handled versions of the 100 series from the 80's & 90's. Came with nylon sheaths. The 619 and 639 came in both black and olive drab.There were lots of pictures here at one time but most went the way of PukeBucket. Always wondered why they could not come up with a 'MATE' name for the Skinner.
602 TrailMate (102 Woodsman)
603 Kraton Skinner (103 Skinner)
605 PathMate (105 Pathfinder)
619 WoodsMate (119 Special)
620 CampMate (120 General)
639 FieldMate (black)
639 FieldMate (olive drab)
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Casual observation to me is that the Olive Drab (OD) color might be a little less common but not rare. I've seen OD only on the 619 and 639. Interestingly the 619 is named differently for the 2 colors, Olive Drab (OD) called GameMate and the Black (BK) one called WoodsMate. The black handled knives came with black sheaths and the olive drab with camo. There were some 639's made without the saw on the spine and are less common. What must be very rare are the 619's in other colors, prototype samples only. Brown, Green, Gray, and Orange. I've heard of them but never seen one.
The handle is Kraton, a synthetic rubber developed by Shell Oil in the 1950's. Most rubbers get slippery when wet but Kraton seems to get tackier, a good property for a knife handle. The knives in my collection only cut air but Haebbie reports that the rubber handles loosened on knives that have seen hard use.
There.... that's all I know.