Dave: Is there some meaning of 'may' I am missing?
There may be. I believe that my usage of 'may' in this particular context was correct.
From The Macmillan dictionary
may . . . but: used when you agree that something is true, but you argue that this does not change the main fact that you are stating
The school may not be as good as it was, but it is still popular.


Cheers