months sort alphabetically even though I selected custom order

It's me with the cemetery records again. Thank you BrownBoy for the suggestion to put the year and date in separate columns.

I have month and date in one column and year in the next. I tell it to sort by the year column first (sort on values, A to Z), then the month and date column (sort on values, custom [January, February, etc.]). All the cells are formatted as text; in the sort warning window about numbers stored as text I've tried both ways. The year sorting is fine; the months are sorted alphabetically. Example: August 3 1968, July 24 1968, June 15 1968, May 18 1968, October 29 1968. A weirdness is that when I copied those particular cells onto a new worksheet and sorted them the same way, it was fine (May 18 1968, June 15 1968, etc.)

Thank you in advance for the help!