I do use the combobox_change method for one combobox but the dropdowns I was referring to are in-cell via excel validation.
I have been able to resolve the problem and it boils down to this:
There was both corruption in the sheet as well as a limitation in Excel 97.
To solve the corruption, I was able to bring up an old revision of the sheet without the worksheet_change problems and copy over the new code. That worked except that cells using dropdown lists via excel validation still didn't trigger worksheet_change events.
After some research, I found this article
that explains how said lists don't work in excel 97 and it's a known issue. I fixed this using worksheet_calculate as mentioned in the article.
Thank you for your help!