2005 Plotting oddesy

All right folks put on your thinking caps.
We received plans with titleblock drawing xreffed in. All went well
until plotting time. The drawings would not plot according to our .ctb
file. All lines came out the same line weight - light. So I removed
their titleblock and replaced it with a older one that I had already
removed the heavy attributes. Their titleblock had information I could
not change, but the date would be inserted after plotting and the
drawing number would change if I renamed the drawing.
The drawings plotted fine and I was a happy, if not frustrated girl.
However, after working on the drawings on a different machine, the
plotting issue re-reared its ugly head. I could not finesse the
drawings a second time and had to copy the 90% drawings and re-do the
work to get them up to 100%.
What did I miss in all of this mess? It put me in a foul mood for the
rest of the day.
Janice