Thanks for the good comments on this tough subject.
Certainly, testing can shed light on the situation. We use Idared as our tissue test "subject", since that variety gets bitter pit severely here (oddly, Honeycrisp has not so far). In 2018, a bad bitter pit year, it showed low Ca, K, and Mn. Soil tests tend to show low pH and calcium; high K and Mn.
We are throwing the book at it--increasing compost applications from light to moderate, putting on high calcium lime, and spraying lots of foliar Ca and a couple sprays of foliar Mn. It seemed to pay off last year at one of our two sites, where we had no bitter pit. It was still bad at the other one.
Brandt, I think nettle tea has some quickly available Ca, but much less than a full-strength Biomin Ca spray, so I would include both.
We'll see what this year brings!
Hemlock Grove FarmZone 5 in New York