I've heard sometimes climber's will wait until their roots are so big before blooming. So it might take them longer before they bloom. See what next year brings :)

Since it is from your neighbor it will be easy to check the rose by comparing the two. take a leaf set over and check with his. Also compare thorns, color of new growth and so on. Does your rose get sunlight? Is it still one cane or has it grown more canes from the bottom yet?

It has multiple canes and it gets good sunlight. I will have to compare leaf set to leaf set in tomorrow's daylight. His is on a southern exposure, but mine is on an eastern exposure. Maybe that makes the difference?

So I went and compared leaf sets. My eye is not trained enough to see a difference between leaves. However, what is glaringly different between the two is that his canes and branches have very few, but large thorns. My canes and branches have smaller, sharper thorns but are COVERED in them like hair.

On his branches you can pinch a branch between the thorns without getting poked. On my branches it is impossible the find any bit of branch to pinch between your fingers that would not poke you with multiple small sharp thorns.

Does this signify that I actually have a DIFFERENT rose tree that propagated off his root stock instead of the actual rose I see blossom in my neighbor's yard?

Yes, you have something different. But I not sure of what you have. Where are you from? Different root stocks are more prevalent in different areas. I would get rid of what you planted. It's surely disappointing after such a long wait. Perhaps your neighbor would let you root a cutting instead.

It doesn't sound like rootstock. A chance seedling is more likely.

I agree on the seedling but since it has not bloomed in three years. I'm not sure I'd have the patience to keep it any longer. However it can take a new climbing rose that began life as a single stem with a couple of roots a while to flower.

Well, I don't think it was a seedling because it was attached to (growing from) my neighbor's rose when it was removed. It was just growing near the base so low that it sprouted its own roots. Must be root stock.

To answer your question I live in the Detroit, Michigan area.

Is the neighbor's rose possibly Climbing 'America'? If so, that one is readily available, and is a fast grower even from a body bag. If it were me, I would spend the $5 for a sure thing rather than wait 2 years for something that could turn out to be root stock. But that may just be my old age showing...