Are you referring to college ROTC? HS JROTC? Presumably for this category of service academy nominations?
“Principal nominee” usually refers to one of the ranking methods used by elected officials for their slates of nominees. I have not heard it used in connection with either college ROTC or JROTC sources.
If you get a nom from a ROTC source, you have a nom on the same basis as all others in the category, and you are competing against all others with that nom, nationwide. There is no way of telling how many earn that nom in a given year for any SA which can use those noms.
See page 7 in the link below, which specifies the number of appointments that can be charged to this category of non-elected official noms.
The nom should show up in your portal, which is perhaps what you are referring to. Continue to work for other noms. In due course, the SA will review your application, determine if you are fully qualified and if they wish to offer you an appointment, and if they do, will charge it to one of your nom(s). That can happen between now and 1 May.