[mikeash]

Why would you give up and say "failure to validate" just because someone didn't answer the phone or had moved away?

I'm proposing to actually put some real effort into this. If they no longer live in the area, find out when they moved. If they don't answer the phone, track them down. If they're dead, find out when and where they died. For the difficult cases, get some boots on the ground and figure it out. Let's take your numbers and say that 900 of the cases are easy, and 100 are tough. If you dedicate $10 million to the study, then you can spend almost $100,000 to figure out each of the tough cases.

This is well within the resources of a university research team or a lobbying group. If a major political party is convinced that voter fraud is a big problem and needs to be addressed, they could easily front the money needed to come to a definitive conclusion. An electoral commission could do it on a non-partisan basis.

I'm not aware of any such research either. If it's been done, the result has been too boring to report on. If it hasn't been done, then my question remains: why do you want to enact such a major law without doing the research first?