There isn't any relevant document found from the webpage. thanks a lot for any hint.
I went back to a single code-base approach. I had had it split between 2.x, 3.0-2, and 3.3+ because I liked some of the enhancements in 3.3, but it was too big a headache trying to keep three versions in sync.
Edit: I also changed from using the strings 'read-only' and 'read-write' for opening databases to the constants dbf.READ_ONLY and dbf.READ_WRITE.
0.97.001 now supports opening databases as read-only even when the files are read-only (yes, that was a bug.)