My apologies MATKAT I did misread your bits, blame it on the fumes!
As for NLG pins I have experience on a few occasions of NLG fitted to 747’s on pushback and they have forgotten to pull them and the aircraft have had to dump fuel before landing to have it removed. (Not me and Companies I have not worked for)
Reference: the fitting of NLG pins for push was that some aircraft depressurise their systems so the possibility of a pull forward etc could collapse the NLG. This possibly answers the question why not fit all?
So I think basically that it is some Companies requirements that they either do or don’t?
The normal requirement for towing is fit all and tech log it.
For push and towing most ground handling companies have their own pins so that is the ones that do not go in the tech log hence the incidents above.
