As Roman Schmidt points out note that 34055 carries the smokebox numberplate from 34043! He adds
"34035/43/55/74 were withdrawn in June 1963. 34055 was already at Eastleigh, followed by the arrival of 34043 around August and subsequent scrapping in September.

For a period between withdrawal in June 1963 and scrapping in April 1964, 34055 was used on steam heating duties in the Works yard. A plausible explanation as to why 34055 carried the numberplate from 34043 might be that the smokebox door on 34055 was found to be defective and replaced with the one previously carried by 34043."

Because both locomotives had been withdrawn and were due to be scrapped, fitters carrying out the smokebox door exchange as likely saw no point in removing the numberplate too.