Artist thumbnail missing in iTunes

This has been questioned many times. I'm using iTunes 12.9. Some people have responded that it's a purchased/not purchased issue. That doesn't seem to be true. Here is what I found...

If you put artist name under Album Artist you have a chance of successfully adding the Artists thumbnail. The trick here is putting the artists in correctly. For example Beatles will not work. You must put in The Beatles and the thumbnail will appear.

My question is, How do we find the correct spelling of the artist name? An example of how this can be tricky was the name Booker T and the MG's. It required me to put it in as Booker T. & The M.G.'s, with the periods in the correct places.

So does anyone know where we can find a list of the artist names and the correct spelling. By the way, I tried right clicking the artist and selecting show in iTunes store. That brings me to the artist but doesn't resolve the problem. For example, The Box Tops. Fairly well known band. Info on them in the iTunes Store. No picture under Artists. I've tried The Box Tops and Box Tops without success.

By the way, it's a small precentage of artists without pictures. I have been able to figure out most of the names and have pictures.