On 30 Nov 2015, Ed Pawlowski wrote in
alt.home.repair:

You do know that many of the numbers shown are not the number the
caller is using? Blocking them works today, but they have a
different one tomorrow.

Yes, I do. That's why I log them all and don't bother to block a number
until it shows itself to be a repeat offender. Which does happen more
often than you might think. OTOH, many numbers get used once, then
never again. They would be a waste of time to block.

My records show that use of a number can go in cycles - it may be used
for a few weeks, then disappear, never to be used again. I've also
found a few numbers that have been used by different scam campaigns
([s]campaigns?)