This is a post repeated from a Facebook post on Monday, June 17 (one day after my 50th birthday). I have added annotations and changes in red.
Dear Facebook Friends,
Thank you for the Happy Birthday greetings!
Turning 50 is very strange! First, it is half a century. But second, I really
don't feel 50 (I somehow got stuck at 30 mentally, or maybe that is 35 now).
Here is a very short study of the phrase "Happy Birthday!" I will try to work
on it a little each year.
A Study of “Happy Birthday”
1. Happy birthday to you!
2. A happy 75th birthday to you!
3. *Happy 75th birthday to you!
I no longer think this is ungrammatical.
4. A belated happy birthday to you!
5. *belated happy birthday to you!
6. A happy and blessed birthday to you!
7. *Happy and blessed birthday to you!
8. A very happy birthday to you!
9. *Very happy birthday to you!
Generalization: Determiner drop with “Happy birthday” can only apply if “happy”
and "happy birthday" are unmodified.
10. Nice shirt!
11. Nice car!
12. ?A nice shirt!
13. ?A nice car!
14. Very nice shirt!
15. Very nice car!
16. ?A very nice shirt!
17. ?A very nice car!
18. Nice second shirt!
18. Nice second car!
19. ?A nice second shirt!
20. ?A nice second car!
Regular determiner drop (RDD) in English does not obey the same condition as “Happy birthday”.
In RDD, the adjective can be modified as in 14.
21. I wish you a happy birthday/a happy father’s day/a merry Christmas
21'. *You a happy birthday/a happy father's day/a merry Christmas
22. *I wish you happy birthday/*happy father’s day/*merry Christmas
24. What a nice car!
25. That is a nice shirt!
26. *What nice car!
27. *That is nice shirt!
Both kinds of determiner drop are blocked phrase internally.