I ran into the same thing when I left VWS. I ran Cumulus for a little while, then added WD to the mix so I run both. But I had data going back to 2004 in the same CSV files. Then I had about a 2 year gap. I remembered that was about the time I moved to a new PC with VWS. I think a setting didn't get tripped up on the move. Those CSV files are small, and I wanted a copy for each year. But after the move, I'm guessing that setting didn't stick.
But I was able to use the WD import from WU to get the data. With WU sucking a$$, I'm not sure that import will still work. But my VWS CSV files imported perfectly.