Yes, good point, but then how to structure a single formula that will deal with both possibilities and give a meaningful result? ISTEXT will be false for both and ISNUMBER will be true for both. YEAR gives the correct result when applied to the Month and Year combination, but when applied to the single four digit year it treats it as a Julian date and gives "1905". The only thing I could come up with, since none of the dates will be from the early 20th century is the following:

=IF(YEAR(E3)>1950,TEXT(E3,"mmmm") & TEXT(E3,"yyyy"),E3)

That should do it!

Thanks for your help!