Apple to Zelkova

This year our old apple tree produced a bumper crop. As you can see from the apple in my hand, it's an odd-looking fruit--nothing at all like the apples in the market. We never spray the tree, so they are wormy and bumpy, but if you want to eat just half a crisp, delicious apple and take in absolutely no pesticides, this is the one for you. These apples need a long time to ripen and were too sour and green to eat until recently. They are delicious now that it's November. Does anyone have any idea what variety it might be? The tree was one of only a couple of trees that were our property when we came here.
We have planted a veritable alphabet of trees & shrubs in our yard since moving here 16 years ago. Here is the list, to date:
Apple (3 varieties), Arborvitae (2 varieties)
Buckeye, Buckthorn, Burr Oak
Caryopteris (blue mist shrub), Cedar, Cherry (Nanking shrub), Crabapple
Dogwood
Elderberry ('Black Lace' Sambucus)
F
Ginkgo
Hawthorn, Hemlock
I
Juniper, Japanese maple
K
Lacebark Pine
Maples (Silver, Sugar)
Nanking Cherry
Oak (Bur, Pin)
Pear (ornamental and Bartlett), Pine (White, Lacebark, mugho)
Q
Redbud (Forest Pansy), Redwood (New Dawn), Rose (several)
Spruce
Tuliptree
U
Viburnum
Washington Hawthorn
X,Y
Zelkova
Apple photo by JulenaJo.