Again, thanks for your quick and thorough help. My module name is different than my function name, so no problem there.

I appreciate your suggestion for getting past the qualified function references. With more than 50 workbooks containing references, that's a bit of a pain, but then this whole thing has been a pain. Since last looking at your response, I have discovered that I can open each workbook, click Edit Links when prompted, select the UDF workbook, click Change Source, browse to and select my xlam file, click Update Values, and save the workbook. That too eliminates the qualified function references. Fingers crossed this problem doesn't come back again.

There seems to be no doubt that Excel or some other part of Windows is storing some value that keeps it from automatically picking up the most recent version each time. Who knows where that might be or how to overcome it (if that's even possible).