TL;DR - the A/C blew cold this entire trip and seems to be going strong.
After a couple attempts at fixing the A/C, ultimately replacing the evaporator core (and other inside-the-cabin components), the receiver/drier, and ultimately the compressor, I think the A/C is working now. I'll keep monitoring it over the next several months, and I have a new condenser and some Schrader valves on hand in case I need to replace those.
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