I've seen the biennial-bearing on some of our older, un-named crabs, but haven't noticed it yet on our newer (2013 - 2019) trees yet. The older crabs were purchased from a Pa. Game Commission seedling sale years ago. They get 1 1/2" to 2" crabs on them. We don't thin them.
So far, our Winter Wildlife crabs have put on fruit every year, but they're still young trees. Time will tell what they do going forward. Violi's has been iffy on producing, but it isn't in a prime spot. All Winter Hangover crab (SLN) seems to produce every year so far, and so has Nova Scotia crab (Morse, 2013). Centennial seems to produce every year, but I think the crows or coons get them even before I can eat one. We had 2 Trailman crabs - one died last year with NO visible damage/disease(?), and the other one is too young to bear yet. The older Trailman was a good producer each year.
FWIW - last spring I planted a Sugar Tyme crab in our back yard, and it was covered in white blossoms. This spring, there are only 4 blossoms on it - but we had some REALLY crazy temperature swings, going from 72 down to below freezing a couple times. We also had pea-sized hail, very high winds, and loads of rain. Sugar Tyme is a very highly rated heavy bloomer/producer with great DR. It's a bird crab/ornamental. I'm wondering if this spring's wacky weather has had an effect on buds & blooming. Our Profusion crab in the side yard is coated in reddish-purple blossoms. ???