Is it possible to have two different service numbers? Probably not
.
In WWII I was 1132877 as an airman.; 156066 as an officer (both in RAFVR)..
Went out in 1946, 1948 commissioned in RAFVR as a Flying Officer, kept my 156066. Came back in on a SSC in RAF in 1949, kept 156066, also when got a (laughingly named) "Limited (ie Nil !) Career Permanent Commission" in 1955.
Counting retired service, now a Flt Lt with 68 years seniority. Anybody beat that ?
("
He started at the bottom - and liked it there").