What is on the card, and who decided that
Nobody. There is no standard, no issuing authority, and no required field. Every card in circulation reflects a design decision by whoever printed it, which is why two cards for the same animal can look entirely different and both be equally valid - or equally meaningless, depending on how you use them.
Your name
Identifies the handler. Useful in conversation, irrelevant to any legal test.
The animal
Name, species, sometimes a photograph. Helps a neighbour connect the animal to the household.
A reference number
Looks official. Points at the issuer's own records and nothing else.
An issue date
Occasionally present. Does not create an expiry, because there is nothing to expire.