Thanks for the Yellow Bellflower test. They're an old variety, dating back to 1749 in New Jersey, and are claimed to be extremely long lived and growing very large. Fedco has stock on them.
Air flow is everything when it comes to nice finish on apples. You should cut down all that grass far around and underneath the trees. Then mix compost & manure and put it down around the base. Then if you can get some tree trimming wood chips (most of the time they are free) then put that on top.
I'm on the East coast and have had several frosts including this morning, and picked some Keepsake about an hour ago which were good. It has that same rounded look like the Keepsake shown but yours look darker. I've noticed that the stem if pushed to one side with a thumb snaps readily, so much it's incredible what a good hanger it is. The flavor is incredible, lots of sugar and acid and flavor. Medium scab surpassed by Pink Pearl (worst) and Lyman's Large Summer. The Lyman's and Keepsake have yellowish flesh going to green white on Keepsake. Definitely try that one again if you can. The Lyman's has beautiful flavor too but I spend more time on that one tree...the leaves get mold or mildew or whatever. Thanks.
If your Zone 4b is like a Midwestern Zone 4b, late ripening apples (unless they ripen well in storage, in which case they can be picked early, before frost) are a big gamble due to a shorter season and early frost. The tree is likely hardy, but the fruit would likely be ruined by freezing, and may or may not be salvageable by cooking into sauce/butter or pressing for cider. I am not one to gamble like that, but if you have enough land, perhaps uncertain harvests would be OK since there is space to plant other varieties to be your workhorses.
