I'm not sure if this is helpful but last summer I paid the CAA to issue a personal registration for my aircraft. Initially I phoned and asked if I could have my desired reg. to be told that it had already been issued but was no longer in use. When I asked if I could pay to reactivate it I was told that once issued that registration had to stay with the original fuselage and could never be used again, even if classed as 'de-registered'.
Luckily I phoned again on another subject and in passing asked if my desired reg. was obtainable by any means and was informed that the first call had been a mistake and my registration was available. On G-INFO selecting either old or new registration takes you to the current entry for the aircraft with clear indications of its history.