Hey guys I am hoping to find an answer here as I can't find it anywhere else and even the dealerships couldn't tell me the difference...

I am trying to sell my stock cats from my 2009.5 G8 GT. Part numbers stamped on my cats end in 7817 & 7816. From that same year (I assume before the redesign), there were converters produced with part numbers ending in 1315 & 1316.

What is the difference between what I assume are the 2009 cats (1315 & 1316) and the 2009.5 (7817 & 7816) cats?

Everyone interested in buying them only want the 1315 & 1316 cats but NO ONE can tell me what the design difference between these 2 types of cats are...