Thanks! You are correct, however, I couldn't solve the issue by excluding records with a space in that field because the field was contained within a text box. Mail merge rules don't function the same way for fields in headers, footers, text boxes, etc.

My workaround was to create a column header/merge field called Blank, write a similar formula with blanks and spaces, insert the field "Blank" into my document, NOT in a text box, and eliminate records with blank spaces.
=IF(ISBLANK(B3)," ","")

It was a weird set of circumstances, but this worked.

Thanks for your help. You brought me over the finish line.