I've been using up a lot of canned food lately, with many of the tins having 'best before' dates that expired well over a decade ago. I've enjoyed the contents of all of them and I've been unable to notice any degradation at all in their contents. So I'd have no problem with eating tinned rice pudding that's 6 years over date.
The can of rice pudding I ate yesterday was only 2½ years beyond the date on the base of the can though. The contents were brown because it was Ambrosia's 'traditional' one:
https://tinyurl.com/y9blf7gz
Maybe that's what you've got?