To be pedantic, the 501 and 551 (and 525 series) are single pilot aeroplanes, all the rest (500, 550, 560) are two pilot aeroplanes. However, in the US the FAA will give you an exemption to fly these single pilot if you meet various experience and training requirements. In theory the exemption is registration specific, although I've never heard of this being checked. It is this exemption that is usually not recognised outside the US.
As an aside, JAA does not have any actual authority over licencing - that is still down to the individual NAA's. In theory they have all agreed to implement the JAA standards, but in practice none do so exactly although some are closer than others and have been listed as "JAA compliant". It is because of the failure to do as agreed that the politicians have started EASA to take over. Basically in trying to hang on to their empires the beaurocrats have managed to not only lose their battle but saddle us with another costly layer. Well done, chaps!!
