Many programs that we all use for CRA will only take 9999 (part of the geocoding issues). Or I guess 99999 this year? 999999 next year? anyhoo
So for many of us, we enter 9999etc in our geocoding software and CRA analysis programs because the program defaults won't allow NA.
When we submit, most of these programs convert the 9999999999 entries to NA which is the only allowed entry for submission.