In the document series called 'Flugzeugunfälle und Verluste bei Schulen und sonstigen Dienststellen'.
The units with numbers ranging from 101 - 11x were what one could translate to operational training units, and were reported as such.
A couple of examples:
http://www.ahs.no/ref_db/lw_loss_pub...?lossid=107194
http://www.ahs.no/ref_db/lw_loss_pub...?lossid=100985
F is Feindflug. (Heimflug and Feindflug). This is an indication on the mission flown, not an indication that enemy action was involved. One example is of course an aircraft lost due to pilot error, while on an operational mission. This would have an 'F' attached in the loss list, but no enemy were involved (other than by inducing stress....).
The categories 20 and 21 cover this situation in the Summarische Verlustemeldungen, 20 being 'ohne Feindeinwirkung mit Feindauftrag total', and 21 being 'ohne Feindeinwirkung mit Feindauftrag beschädigt'
Third - you did not make three points. You simply quoted information from three different sources stating as your point that these three references (two books and a webpage) must be the proof that the Luftwaffe original documents are not to be trusted. Sorry - but that doesn't quite cut it as a scientific evaluation of the available sources, at least not to me.
Regards,
Andreas