rear seat on blazer different for different years?

[Webwillie]

Hey All
I have a 1972 Blazer 4WD that I am about 95% done on the frame off resto.
I have had truck for a long time. Was a daily driver and was what I carried my young family around in. What I am curious about is I bought a complete re-upholstered seat set out of an era correct blazer/jimmy. I have noticed, though that my original back seat has 2 more mounting brackets on the back side (tail gate side) than the one I purchased. Other than that , they are identical. Mounting brackets are the same, etc.
Is there a difference on the model year on these seats?
Thanks for any info you may have