Seven is a magic number all right, but it also is a number that the human mind can readily recognise - these facts are probably connected! If we see seven items, we can identify them as seven, but if we see eleven we just see "a lot". Obviously, seven is near the upper limit - it's easier to recognise without counting if there are two or three items.
So that's probably where the idea came from. As for stable personalities - yes, they are worthy things to have, but probably more likely to come from having a warm, stable home. Having said that, and assuming that you are pretty stable yourself in spite of having two letters missing, why not just read quickly down the top 100 names in the year of your choice (go to the Home page for instructions), note the ones you like, and then see if the spelling is what you'd prefer. A choice between Deborah and Debra, for instance, could easily be resolved; or Stephen and Steven. Annette and Anita. And so on.