Special duties has always been a cover-all euphemism
I believe they also included some of the other Int disciplines e.g. Photo Interpreter back in the day when the Admin Branch did a lot of them rather than having a specific Int Branch
and he's hardly claiming to be the second man on the balcony
I've always wondered how big a balcony the Iranian Embassy actually had. If everyone who claims to have been there actually was there, then frankly I think the balcony on its own would have been big enough to warrant its own postcode!