7501 yes, 7499 no. The digits of the transponder only go up to 7. Therefore, 7777 would be the highest number the transponder can go. 7500 is hijack, 7600 is nordo and 7700 is emergency.
Thanks for that information. It would be interesting to learn if the same number of passengers who started the flight complete it after the plane's Canadian sojourn.
Hmmmmm, It's octal?