Having used cars before with shim tappets, I would say 30,000 miles would need to be checked, they have a large surface area, so don't go out of adjustment so quick as people think.
Escort/fiesta/modeo diesel soldi tappets fit straight in, and then the shims from peugeot/vw/audi/seat/fiat/volvo/ford and a few others fit straight in, NOTHING needs removing to fit the shims, if you are careful, as you can push the bucket down enough to create clearance to lever old one out of seat and new one in.
Just a bit of simple faffing around with a feeler gauge, then take all shims out to see what gaps you need/thickness of shims, you can do swappsies as they do not need to be new, as they wear perfectly evenly, so cutting down on the ones you need to by.#
The last escort 1.8D I did needed only two to buy, £3 each.
tabetha