Hi Stig,
Well I wrote a long answer about how Grosz would have mentioned the 'missing' 269 series aircraft 269.73 to 269.76. However, I then did a search,and my apologies it seems you were correct
https://mnl-gov-hu.translate.goog/mn...n&_x_tr_pto=sc
Zoltan Csirok also mentions 269.75 in this more detailed article,so pointing to the existence of the other 'missing ' serials.
https://iwk.hu/_userfiles_/aviatika/...bertfalvan.pdf
Regards,
Clint