67-72 bench seat question

[lolife99]

Are the bench seat frames and different between the 67-68, 69-70, and 71-72? I'm talking about the bottom of the seat with the upholstery removed. Also are the bolt on adjustable tracks different from year to year? (I'm not talking about buddy buckets)
I bought some new seat upholstery for my '69 and the bottom seat upholstery is 1-1/2"-2" too short on the back side. (too short to hog ring into place).
My upholstery guy thinks it's sewn wrong since he just did a set for a 71 with a kit from LMC. Mine is PUI brand upholstery with the stock scroll pattern for a '69. The seat I am recovering has very nice foam and will fit really good except the material is too short.
Any help would be appreciated.