Hi JimG,
Sounds like 17 years in, your CH had a pretty established pattern of behavior.
The weird thing is, it turns out it's common to be hit with a pattern shift you never would have expected, even after umpteen years of predictability. One of the most common shifts is the lengthening cycles BTW, so It's probably not worth worrying about chronic for another few months at least.
Lotsa headbangers are convinced the usage of triptans can cause cycles to lengthen. I've been episodic for going on 37 years, so I had 12 years or so of CH joy before triptans hit the market in the US, and what I found was my cycles kept lengthening and lengthening before I ever tried a triptan. I had been on some heavy cocktails of other prescriptions though.
Here's hoping you'll be 12-ish weeks and done this time, with a sudden cessation, or at least you'll see it tapering off soon, which I figure is a likely scenario. I'll officially place a bet on that right now.