Thank you Alan for Many Happy Returns of the Day!
I never thought I would be one to understand some of these abbreviations...
technomc—
HUBTY could also stand for Happy Unbirthday To You, which is, of course, valid all days of the year except one.
Regarding the question of HEBTY, I have always thought that one might celebrate one's birthday for a few days before, during, and after the actual day.
Which would mean we might need HLBTY as well.