I've got a distinctly large head (an Ecrin Best is pretty much just adjusts large enough for me with the thin padding on), and I can get an Edelrid (54-60cm) on, though it does feel a bit snug, and I'm not sure I'd want to wear it.
One point I would make is that if the issue for your club is absolute age of helmet rather than years of use, better check the helmets when you get them - I moved some lights for a club from Vertexes to Edelrids (still got a stray one left to do.
They bought their helmets last year, but the one helmet of theirs I have left to covert has a 2011 label inside.
For the Ultralight, maximum manufacturer lifetime is 12 years unused in optimal conditions, or 10 years usage with 'occasional and appropriate' use.
But if you're constrained by a one-size-fits-all 5 years from manufacture, if you're buying Edelrid helemets, best make clear to the seller that you require recent ones - there was someone on Amazon USA mentioning helmets that they had bought were a few years old, though that clearly wouldn't be an issue for many people following manufacturer's guidelines, assuming storage conditions were good.
Also, if anyone happens to be wanting to mount Duos on the highly-ventilated Edelrids, some penny washers might come in handy, to allow one of the mounting screws to use an existing hole, rather than having to try and fit both upper battery box holes between the pre-existing ones.
M4x15mm seem sufficient, though M4x20mm would be OK as well.
EDIT: changed lifetime data after locating on Edelrid site.