I would note that pre 1926 ish, I'm told that the Britishpractice was to use the barrel serial number as the master serial number - and have observed several actions with cancelled original serial numbers "force matched" to the barrel serial number.
So from that observation, the Canadian practice of using replacement receivers was similar to an earlier British practice.
Bare Long Branch No4MkI* actions dated 1944 + 1945 were available from ord. stores with no serial numbers.
1954,55 & 56 dated Long Branch actions usually show out of year sequence or LB manufacturer serial numbers, demonstrating that they were ALL? Used simply as replacement receivers rather than for any production run.
This practice extended to (i've been told) Inglis High Powers and I have seen FN C1 & C2 rifle receivers with no original serial numbers.
Having said all of that, nearly all of the Long Branch No4 rifles that I have personally seen with Savage (or out of sequence/manufacturer) serial numbers show signs of the original serial number being removed.