Thanks for the confirmation about the facts.
Why is it a problem? Uber tried to use the new card three times (for one transaction), two weeks before my existing card expired. JLFS declined the transaction three times (and didn't tell me). Uber told me on the third transaction.
How am I supposed to know which suppliers are going to upload the new details, when?
The bottom line is, as I implied in the title, and specified in my OP, effectively (for some transactions from certain big customers of the issuer) your credit card does not expire at the end of the expiry month, but shortly after you've received the replacement card. That's ok, if the issuer tells you that. They don't. Perhaps they should.
OK, sounds like there was an unfortunate cock up in your particular instance. The new card details should only be sent by the issuer and used by the merchant when you have activated your new card.