Yeah, I think you are misunderstanding something here.

Yes, there is a non-zero chance that spare bits will be identical. But that's only relevant, if you have a bug in your code wherein you are trying to use a destroyed handle. If you are never using a destroyed handle, then the spare bits being identical is completely okay.

Another way to think of this is that the spare bits are optional. The interface is good even if there were no spare bits. The spare bits only add an additional probabilistic security check.