Other sources such as the Manchester FHS said that it was
"temporarily mislaid"

It is hard to imagine how records for some 50,000 odd people got lost without some record
such as being accidentally destroyed, burned in a fire or mislaid and lying in the back of some warehouse.

The National Health Services records for the UK were originally based on the 1939 National Registration but of course are constantly updated,

What was the data basis on which the IOM Heath Services .
were first established?
.