date formatting in Access

I wish to format a column for month and year only. These dates include prior
years and the current year. When I select "date/time" and format it mm/yy
and type in a prior year like 11/05, (november 2005) Access changes 05 to 06,
the current year. Even when I select "Number" as the type of entry, and
format it the same, mm/yy it does the same thing coverting all pervious years
to 06.
I want to be able to sort by date assending or desending and these items
only have month and year. I can do it with two separate number columns, one
for year and one for month, but that requires two sorts which is not as quick
an easy as I would like.

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