It seems odd that they haven't solved the "machine readable" part in some other way decades ago. You only need a handful of bits of data-- 12 bits would probab

It seems odd that they haven't solved the "machine readable" part in some other way decades ago. You only need a handful of bits of data-- 12 bits would probably be enough to encompass all likely stamp denominations. You could overprint print a simple lined barcode for 12 bits of data in, say, UV-flourescent ink and not mess with the existing visible design. This could have been silently done 20 years ago, so by now, only a tiny selection of really ancient stamps were unusable. There's no reason for the big chunky barcode unless they're trying to track use of individual stamps (which seems a bit Orwellian), or as some sort of convoluted anti-counterfeit device (compare Euro banknotes, which include embedded check digits in the serial number, so not all numbers are valid). The other drawback I could see would that it changes the footprint. On something like a postcard or a tightly designed marketing flyer, you might want to use every available square millimetre.