This site gets alot of traffic and I thought it may be a good location for a database where concertina owners, using their "account user name(s)", could list their instrument(s) with the accompanying serial number(s) and any other identifying specifics i.e.: color, style, bellow folds, blemishes etc..
Such a database will not prevent loss (or theft), however, it at least could help in tracking down the true owners (on a Global scale) of missing concertinas. This could be of significant help when "suspicous" item turn up for sale in all the usual places.