Are you using a standard field with auto-enter by calculation instead of a true calculation field?
Yes, I was using an auto-enter by calculation.
When I read your response, I went back and changed it to a "calculated" field, and it solved the problem!
(I did not that you could have a field's value calculated two ways...)
Sometimes, you may want to keep that field as an auto-entered calculation. In such cases, there's a trick you can use in most cases that will force Filemaker to update the value stored in all records that existed prior to the change in the calculation: Updating values in auto-enter calc fields without using Replace Field Contents
Thank you all!