There is a famous motor museum not to far from me which has definitely sold / swapped vehicles over many years, and at one stage had sold many of the original registration numbers to collectors, or in small print expected a 99 year lease of the vehicle loaned to them for restoration / display.
Some museums are left exhibits as long as they are never used/driven again by request of the donors.
A lot of small items...medals uniform items are stored away never to be seen again or lost in storage ?
Ashley