In general, I've found that per-weird-input-format date management is
troubling, because there are so many and many of them overlap.  It's
worked better to define a year variable, which contains the
preference-order (meaning, your preference for what test to believe the
results of) attempt to extract a year value and with a default of "nope"
so failure can be detected, and then the same with the month.  The
template then checks for failure and if it can, returns the assembled
year-month pair composed in whatever format's appropriate.

-- Graydon