The fact is that when you send in the one side of A4 form for revalidation of SEP, it gets scanned and put on file, nothing more.
You could be flying around illegally, with a licence signed by your mum for all it matters, until something goes wrong and they look into your records, and then they throw the book at you.
If I were you, I'd go back through your records and look very carefully. If it is really just an instructor who's been signing your ratings page, and not one who also happens to be an authorised examiner, then I would get this fixed before I took to the air again.