That's interesting!It disappears pretty fast in water with 0 FC and low dissolved oxygen. I suspect those of us who routinely see CYA disappear in the winter months have a combination of 0 FC and short pump run times. It's not something that can be done with water temperatures over 60°F or so. The algae would be insane, especially after the CYA was converted to ammonia.
This is basically irrelevant to OP's question unless an entire season of using trichlor for 50% of his chlorine needs will keep CYA below sane limits.
So, does that mean I could drop my cya a bit over winter without an exchange?