Wouldn't someone who moved have their mail forwarded? That's usually what I do!
I have been working with voter rolls (as an outside vendor, not in the voter office) for 25 years.
I believe that any voter roll in existence in the USA is REQUIRED AS A MATTER OF LAW to keep people on the voter roll until one of three things happens: 1) the voter dies AND someone brings in an official death certificate; 2) the voter moves AND sends a signed letter informing them; 3) the voter does not vote for two election cycles and is first put into "inactive" status, then the next time around if NOT voting is finally purged, the process taking at least 6 years.
If you do as I did and simply call the voter's office where you used to live after moving, they are prevented by law fom removing your name, even if they know you personally, unless you mail a signed letter. So I was on the voter rolls of two states for eight years (one being Broward County FL) because I never sent a notarized signed letter -- even though I had scrupulously informed them of the accurate information.
Still less would they be able (by law) to remove voters just because you did your research and could tell them hundreds of names of people in your neighborhood who were no longer there. This is why I have always takenm voter rolls as being basically official jokes, and why the process of checking voter cards AT THE PRECINCT ON ELECTION DAY is the only way to preserve our way of life.