[Stig Jarlevik]

Quite so Laurent

Reason is that both the two authors (and the website of course) have basically only checked the UK record cards and not specific unit histories.
The further away an aircraft came, ie North Africa, Middle - Far East, the tougher it was to get details back to the UK and thus complete the cards.
Some unit records were also destroyed for various reasons and never made it back in the first place, hence these gaps. I also believe the unit histories from North Africa and later Italy are much more complete than those from the Far East for example.

I don't know if you have the Air Britain range of RAF serial number booklets, but to try and interpret the cards was the initial approach taken by the late Jim Halley. When he updated some of these volumes more unit details were added as they had become known to him.

It is a huge task trying both to read the cards and then also track down each and every unit and correlate the data. Sometimes (quite often perhaps?) the unit histories clash with the cards making things very difficult to interpret.

My hat is off any day in the week for those trying!

Cheers
Stig