Currently Display Name is set as "Erik VII, "Segersäll" Björnsson, King of the Svear".
I checked the English, Swedish, Norwegian, Danish, German and Spanish wikipedias and scanned the profile About section to see where the VII comes from.
English wiki makes this statement "Sometimes, Eric the Victorious is referred to as either King Eric V or VI, modern inventions based on counting backwards from Eric XIV ".
The other 5 versions of wiki that i checked are silent on the matter.
The Swedish kings might be a very good example or a very bad example, depending on how you look at it.
I don't remember the details but the Swedish kings started using the current numbering system sometime in the 16th century. One of the Vasas. Maybe Erik XIV. They adopted their numbers based on a history by Johannes Magnus, which included kings who are now regarded as fictional.
I'll see if I can find a reference.
Good enough, I'm sure.
Wikipedia might be more accessible for some people so I'll add that to the list:
"In the 16th century, Johannes Magnus constructed a mythical line of Swedish kings, beginning with Magog, the son of Japheth, to demonstrate the antiquity of the Swedish throne. On the basis of his list, Eric XIV and Charles IX adopted their high ordinals; previous monarchs with those names are traditionally numbered counting backward from Eric XIV and Charles IX. In contemporary Swedish usage, medieval kings are usually not given any ordinal at all."
https://en.wikipedia.org/wiki/List_of_Swedish_monarchs