The addition of 'asa' to existing four-letter passwords is "announced" on the login page of the NIS web site and in the user guide. I certainly agree that it could certainly be more prominent.
The rules for lengthening your old password if it was
not 4 characters can be found in AIC H32/12.
http://www.airservicesaustralia.com/...up/a12-h32.pdf