What defines an engines year?

[priores]

I was looking at a 1967 Shelby Cobra S/C Replica. The seller said it was a 1967 427 Engine. After inspection it clearly wasn't. Engine block and cam shaft were from '65. Intake was '63. Only parts that were from 1967 were the cylinder heads.

This got me thinking. Is there any type of standard that defines an engines year? Would all the components need to be cast in 1967? Engine block only? Engine and camshaft?

Just curious...

[Mark IV]

The block casting date is the key. Other components are often not date coded.