Well, well, well! After taking a second look, it appears I had not actually made the linking value numeric after all! I could have sworn I had changed it!
I went back for a second look and--low-and-behold!--I guess I was right about one thing--it was something pretty obvious. Operator error. I probably changed the field from text to numeric but somehow didn't save the change. The kind of thing that happens in an unfamiliar interface.
This time, when I went back in to take another whack at it, I found my error.
I also took the time to ensure that the new Record ID (in QB) and the old BigInfoValue (the former key field) had identical values for each record, so I could provide the link from the Record ID to the value I wanted in the child field. It seems like this is a better practice in case more values will be added to the parent table in future.
Thank goodness I found my mistake!
