...The "Feb-06" is generated from a formula using DATEVALUE, MONTH
and DAY vs. just having a date typed into a cell)

what is the formula exactly? I guess the result is text and then it is not
date and will not be found in a list of dates. If the result is really a
date then the day which is is hidden (and potentially the time) of the date
searched is not the same as the one in the list.

Regards,
KL