Are IRS rear end covers dated?

[RugHead]

Bubba touched the one on the 67 and I need to replace. Dang that Bubba!

 

[JohnZ]

They have a visible casting number and pattern number on the upper and lower rear horizontal ribs, so I'm going to assume they also have a casting date also (standard GM practice), but you can't see it with the diff in the car.

 

[RugHead]

Super. Thank you.