Good info here, thanks everyone. Sounds like the takeaway is: ABC doesn't publish an expiration date, but CoralVue lists a 24-month shelf life unopened once opened/capped (not sealed), that clock likely moves faster, especially if exposed to light (mmorrison55's clear glass storage may have sped up the B/C degradation). My high alk reading was probably a mix of aged reagent + needing a recalibration after switching from Neptune's reagents mid-stream. Going forward I'll date my bottles on arrival and buy only what I'll use in ~6 months.
Something to think about but will say up front that this is a personal hobbyist decision. Coralvue is selling ABC reagents. Neptune and CoralVue are competitors. CoralVue is sniping a little bit of revenue from Neptune. CoralVue, if they manage to release the Maven, is reagent based testing. They have said that they are putting barcodes on their reagent bottles to register before use. They also announced the Maven prior to Neptune announcing their Trident NP...
