One thing that has puzzled me, and I haven't come across an answer, is why the Chevy S-10 Blazers and GMC S-15 Jimmys are just labeled Blazer and Jimmy on the board. The Chevy used the S-10 prefix from 1983-1994, and the GMC used the S-15 prefix from 1983-1991 (when GMC renamed the larger model Yukon). These models were marketed with the prefixes, as shown on these brochures:

http://oldcarbrochures.org/NA/GM-Trucks-and-Vans/1985_Trucks_and_Vans/1985-Chevy-Trucks/1985-Chevy-Trucks-07
http://oldcarbrochures.org/NA/GM-Trucks-and-Vans/1985_Trucks_and_Vans/1985-GMC-Light---Medium-Duty-Trucks-Brochure/1985-GMC-Light-and-Medium-Duty-Trucks-09
http://oldcarbrochures.org/NA/GM-Trucks-and-Vans/1985_Trucks_and_Vans/1985-GMC-Trucks/1985-GMC-Truck-11
http://oldcarbrochures.org/NA/GM-Trucks-and-Vans/1986_Trucks_and_Vans/1986-Chevy-Truck-Facts/1986-Chevy-Facts-037
http://oldcarbrochures.org/NA/GM-Trucks-and-Vans/1988-GM-Trucks-and-Vans/1988-Chevrolet-Commercials-Brochure/1988-Chevrolet-Commercials-08
http://oldcarbrochures.org/NA/GM-Trucks-and-Vans/1989-GM-Trucks-and-Vans/1989-GMC-S-15-Jimmy-Brochure
http://oldcarbrochures.org/NA/GM-Trucks-and-Vans/1990-GM-Trucks-and-Vans/1990-Chevy-Trucks-Volume-1/1990-Chevy-Trucks-V1-55
http://oldcarbrochures.org/NA/GM-Trucks-and-Vans/1991-Trucks-and-Vans/1991-Chevy-Trucks-Full-Line-Brochure/1991-Chevy-Trucks-35
http://oldcarbrochures.org/NA/GM-Trucks-and-Vans/1991-Trucks-and-Vans/1991-GMC-Trucks-Foldout/1991-GMC-Trucks-01

I know the 2nd generation models were just Blazer and Jimmy, but the first definitely used the prefixes. So I'm curious if there is a reason for this and any opinions.

Some time ago we were putting the S-10/S-15 label in the chassis field and "Blazer" in the model field, but it is maybe not correct indeed.
Also, it is possible that some lack that info in the chassis field.
If needed, it is easy to change "Blazer [S-10]" to "S-10 Blazer", but those listed as just "Blazer" will maybe require a manual change (or we could rely on the year if present).