That doesn't take into consideration of flaky home-routers (note that they do recalculate the checksum). So the checksum might be processed on bad data. For a

That doesn't take into consideration of flaky home-routers (note that they do recalculate the checksum). So the checksum might be processed on bad data. For a bad connection it will also be quite common that the checksum will happen to be valid. TCP/UDP checksums are quite bad.