No idea on the shop, but the out of date cylinder will not stop you entering any thing, EC will only advise, even at top level, Internationaly and under full ISSF rules.
Rule 6.7.7.1
g) It is the athletes responsibility that any air or CO2 cylinder is within the manufacturer's validity date (maximum of ten (10) years); this may be checked by equipment control and advisory recomendations may be given;
Its now only advisory, and they will tell you its out of date but it will not fail EC. And in practice its now accepted as piece of Jobsworthing that is only in the rules to cover rear ends.
Don't worry about it, best of luck finding out whats happened to the shop.
Walther KK500 Alutec expert special - Barnard .223 "wilde" in a Walther KK500 Alutec stock, mmm...tasty!! - Keppeler 6 mmBR with Walther grip and wood! I may be a Walther-phile?