They don't just expire, and they should be good for a good number of years (although having just got back from the seaside I did see a few rather rusty ones!). The main determining factor I would expect would be whether it was from a Sky Analogue or Digital installation - since the former were pointed to the 19.2 degrees position Astra satellites and the latter are pointed at 28.2. I think the LNB on the analogue setups are no good for DVB-S either (fixed rather than able to switch between H/V positions?).
Old Sky analogue LNBs were H/V switchable as well - but their frequency offsets were different ISTR, and they may have used different switching systems. (ISTR that early Sky 16 transponder systems had to have external band switching gubbins added when more transponders launched?)
An original Sky dish itself is probably fine, though it will be pointing at 19.2 not 28.2 - but if you wanted to watch European TV then there is quite a lot FTA at 19.2, or you could re-point it to 28.2. However you would need to replace the old Sky analogue with a Universal LNB - and you'd need to make sure it was designed for the dish-type you were using (so it was optimised for that dish shape and offset style)