According to lrv:
The green 5OT is called a 5OTG (G is for the Green). It was 1st produced 1991 and dropped in 2002. It replaced the 5OT which has the brown Delrin handles which stopped being produced in 1998.
And a bit more from the "Codger Files" (more than you wanted to know

).
The 55OTG lockback had no real name other than the "Blade Lifter" when it was introduced in 2002. Rather expensive at the time, it was listed at a MSRP of $43.95. It was only produced for two years, discontinued after the 2003 catalog.
Made on the frame of the 5OTG "Green Bruin" linerlock, it was 4" closed, had a 2 7/8" drop point blade with a thumbstud, brass front bolsters and pins, and green sawcut delrin handle with brass "Old Timer" shield. Like the 6OT, it had a brass lined thong hole.
A smaller version, the 53OTG introduced at the same time (and discontinued at the same time) was 3" closed and had a 2 3/16 drop point blade with the thumbstud.
Good news for those who like stainless Old Timers, the 53 and 55OTG's had Schrade+ stainless blades, though the 55OTG was initially listed as having a high carbon blade. Perhaps some of the first ones did indeed use carbon blades, but the catalogs were often filled with detail errors.
In 2003, the 55OTG was called the "Bruin EXT" and the 53OTG was called the "Bearhead EXT". The predecessor 5OTG was first listed in 1991, and was discontinued after the 2002 catalog year.
Several other slipjoint, lockback, and fixed blades had been made over the years with green sawcut delrin and brass bolsters, liners, pins and shields, most notably the factory special orders for the Skoal tobacco promotion. I must admit, the green and brass is a handsome combination.
Both the 53OTG and the 55OTG, having been only produced for two years should find their place among future scarce Schrade collectables. Right now, because of the relatively short time since they were discontinued, and the market glut of factory stock being dispersed, they represent one of the better values out there.
You "may" want to get these other variants to try out too!
Michael