So I'm not sure how this helps me in the future. Even though I had changed the font, there was still some reference remaining. I think I have have copied that word (it was a foreign name) from someone else's email. Somehow that word contained some reference to Calibri. I then simply deleted the word and re-typed it, that solved the problem! I added it to the dictionary but that did not solve the problem. The problem was a single word that was not in the dictionary. I started with a blank document and slowly copied portions of the original document until the problem occurred. Nothing had changed and so I was determined to track down the problem. Then several months later the same problem popped up, but now with Calibri.

I did install the Cambria font and the problem did go away. I first had this problem with Cambria and was told that Word had some 'behind the scenes' reference to Cambria and that I could install the font and solve the problem. Yes, labor intensive, requiring some tweaking of functions, but since I open and close this particular file about 20 times a day, it was worth it. I pasted that data into a blank sheet on the new document and lo and behold, no error! Then within the original document, rather than selecting the table as an object, I instead selected all the cells within that table (this is crucial: this will not work if you simply select the table as a whole, as that will copy the embedded data). I deleted that table out of the new, warning-free document (and checked to confirm that the warning didn't remain when I opened the file). In my case, I was able to do so without error with every table but one (most likely the original I created in Excel). To determine which table(s) were at fault, I copied and pasted them into the new document one by one, closing the file and then opening it on my iPad to see when the warning would appear. To work around that, I created a new, blank document. From what I can gather from the comments in this discussion and my experience, the font Calibri (in Numbers at least) is embedded in the tables, so even if you select all the cells and change the font, Calibri remains buried in the metadata for the table. There is a workaround (in Numbers at least), which is a bit of a pain, but it worked for me.

Get rid of calibri font