When you see an Artist as a related artist to another (Marillion is a related artist to Steve Rothery for example) it shows a different album count from on the actual Artist view.
The Artist view count is often smaller.
I strongly suspect that the Artist view count counts the albums taking versions into account while the related artist link count does not. If so neither count is demonstrably wrong, it’s the inconsistency which makes it stand out.
In my collection Marillion moves between 114 and 79 from memory, but there are a lot of version combinations