Salut!
"Your" Ju 88 is from 1./NJG 100 but the following may have some relevance as the Staffel was formed from 12./NJG 5 August 1943.
For some reason 4./NJG 100 which was based at Tallinn, Estonia used codes beginning with C9(+_M) from at least early February 1944 to March 23th when first W7- code is recorded in Finnish logs. It is obvious that the Ju 88s themselves remain the same - the same a/c individual alfabets + staffel letter keep recurring. Just the unit code changes.
One of my hypotheses is that these "C9" Ju 88s (to 4./NJG 100 and perhaps 1./100 too?) came from IV/NJG 5 which had 16 Ju 88C-6s at the end of July 1943 but none in the beginning of September. For some reason data for August 1943 is missing at Michael holm's site (
http://www.ww2.dk/oob/bestand/njagd/bivnjg5.html ).
It seems 1./NJG 100 starts August 1943 with 12 Ju 88 C-6 while 4./NJG 100 is formed not until December 1943. I have not been able to come up with any logical reason or path for the C9-coded Ju 88s to end within 4./NJG 100. For 1./NJG 100 the logical path would be both shorter and clearer.
Situation may have been the same with III/NJG 6 which used the C9 for a short period after being formed from II/NJG 5. Perhaps there were no paint shops around NJG 5 bases, eh?
Cheers,
Kari