Let's not forget the more useful and less challenging exercise of corresponding codes for:
1. BluRay (HD) and DVD (SD) versions of the same vid (e.g. REBD and REBDB)
2. Censored release of an uncensored vid
A more challenging and increasing important exercise is:
3. Code (and original release dates etc) for the VHS tape of newly re-released-on-DVD titles.
But generally speaking, I +1 and double
@jugulear 's pessimism about these cross-over codes. The studios have something to gain and little to lose by the confusion of us the privating leeches and also the paying customers.