The later(2008) heavier vs earlier(1979) fenders is me.
Both are from GM.
Why the diff? No idea. Both both sets are better then any repop i've seen.

The repop qtr's are from when they 1st came out vs GM qtrs(1979) is just the opposite.
You can oil can and dent the repop's very easily.
The GM's have had stuff dropped, smacked, and banged into them many times over the years without being damamged.
Dont know how good todays repop qtrs are.