Actually, both are still correct. 39-112 is the military serial number of that old bird. When it was retired from the military, someone bought it and had it registered with the FAA (or possibly its predecessor CAA). It probably changed hands over the years. It was then in 1978 donated to the National Museum of the USAF.
If I find a military machine that's been registered, I usually post it with the civil registration so as not to make another profile. Not everyone does that - or even knows to look for one - and it appears Simmermon made a new profile.
Military serials stay with the bird forever - it's just that they aren't always used. Sort of like a c/n stays with them forever also. Only civil registrations change or get cancelled.
All data on the civil registration could be duplicated on the military profile, and just leave the dash out of the military profile to keep it simple, even if it is correct.