It is not clear if you mean four distinct letters or can a letter be repeated?
It is not clear if the letters must be consecutive as in your example or could it be AEJP?
There are only 23 strings of consecutive four letters.
There are combination 26 chose 4, ways to have four distinct letters in alphabetical order.
There are ways to have any four letters(repeats allowed) in alphabetical order.
Here is a separate issue: are we to assume a person has only two initials?