Stamps With No Year.

Yes, this happens with some other countries as well. Most of the time it matches, but if the year on the stamp isn't the same as its actual year of issue, usually the date on the stamp is earlier. The year on the stamp in that case usually represents the year it was designed or printed, not necessarily the year it actually went on sale.

There is a parallel in the coin collecting world, particularly in US coins in the late 18th/early 19th century. They would keep minting coins with a given year date on them until the dies wore out, which in many cases would be well into the next calendar year or even later. Thus that 1802 dime in your collection might have actually been minted in 1803, for example.