Those serial number guides aren't always accurate. They usually are accurate but not always.
For example, I have a Rolleicord that is part of a batch that should have a Schneider-Kreuznach Xenar, when in fact it has a Carl Zeiss Jena Triotar.
What is more important is that the serial number on the front of the lens should match the number on the rear element.
It usually is engraved on the lens barrel, so you normally cannot see it. If you have mismatched elements, that definitely could be the culprit to a soft photo.
If the camera is a bit beat, it's always possible that the camera might have been dropped at some point, knocking the lens out of alignment. With beaters, it's just so hard to say what might have happened to them in the past.
I hope you are able to get the issues resolved.