Thanks much for both replies. The point about "hardcore" is well taken, and the solution using Excel's @ISNA will work great and it will be useful in general to remember that Excel functions are available to me. Thanks again.

I solved the immediate problem today by using Perl's ref function in a test of each cell's value. I am not expecting any references in the cells coming from my spreadsheets. As usual, I don't know why I didn't think of that approach yesterday.

As part of my education into the ways of Perl and programming in general, I do wish I understood more specifics about why #N/A causes the result in Perl that it does. But for now, I'm moving on.