Thanks, Mike. That was the problem (I am new to mac and still finding my way around). I could not see Library in ~users/username so I was getting confused, but now I know I get there by option+Go in Finder. I opened LocalDictionary in Spelling, and pasted in the list of names. In case anyone else is not familiar with how this works, here are two other things I found out:
The LocalDictionary has to be sorted alphabetically, and is apparently not case-sensitive. I was starting with a blank LocalDictionary, so that was easy, but if I want to make changes in future, I will copy the LocalDictionary, add new words, de-duplicate, sort, and then paste back in.
I needed to restart the computer to get the additions to take effect.
It all works now, and because the words are in LocalDictionary, they are in spellcheck for all the other apps I use, which is great.