If you find a Robinson with no decals, this will hopefully help you ID the model or year.
First generation Robinson’s had a gusset with NO “R” stamp. (1978)
Second generation had the famous “R” stamp. (1979-83?)
Third generation had no gusset at all but were still looptails. (1984-88)
GT owned (made?) Robinson’s had a plate welded to the frame’s seat tube with Robinson logo stamped.
Early GT owned Robinson’s were a full looptail and were made in 1987 and 88.
Second generation GT/Robinson’s had a semi looptail starting in 1989?
1987 Pro, Elite, Junior, Cruiser, Mini Cruiser
Pro [Top Tube = 19 1/2"]
1990 Pro, MX, JR
**Specs are from the catalog but I believe Pro,MX to be wrong**
Pro [Top Tube = 18 1/2"]
MX [Top Tube = 18 1/2"]
Elite
Junior [Top Tube = 16 1/8"]
Pro Cruiser
Mini Cruiser
1994 Amtrac, Pro XL, Pro, Junior, Pro Cruiser, MX, SST
Amtrac [Top Tube = 21"]
Pro XL [Top tube = 20 1/2"]
Pro [Top Tube = 19 3/4"]
Junior [Top Tube = 17 1/2"]
Pro Cruiser [Top Tube = 20 3/4"]
94 Notes* All frames USA made and 4130. SST frame fake looptail does not close.
1996 Amtrac, Pro XL, Pro Team, Pro, Junior, Pro Cruiser, Jr. Cruiser, MX, SST , Rebel (Tri Moly)
Pro Team [Top Tube = 20 1/4"]
Pro, MX, SST, Rebel [Top Tube = 19 1/4"]
Junior [Top Tube = 17 1/2"]
Pro Cruiser [Top Tube = 20 1/2"]
1999 Amtrac, Pro XL (Patriot, Missile), Pro (Defender), Junior (Patriot Jr.), Pro Cruiser (Patriot 24), SST, Rebel
Pro XL [Top Tube = 21"] Aluminum, USA made
Pro [Top Tube = 19.95"] Aluminum, USA made
SST [Top Tube = 19.90"] 4130, USA made
Rebel [Top Tube 19.6"] Mild Steel
Junior [Top Tube = 18.13"] Aluminum, USA made
Pro Cruiser [Top Tube = 20"] Aluminum, USA made