Yes, I did. I had warnings turned off, and when I added them in my cutout Perl told me right away that == was the wrong operator.
And of course now it works.
And that infers the answer.
I'm guessing that "15 Jan" worked because it started with a number, where "Jan 15" is a string through and through.
But this particular typo has been in place for YEARS without being caught. Still wondering what changed in Debian land where it stopped working in the last month.
Oddness.