> Regarding your fence, 20 years is very far from enough to establish "urminnes hävd".

I was thinking of adverse possession, for which the time limits are 20 years or even 10 years in some cases:

https://jdc-definitions.wikibase.wiki/wiki/Adverse_Possessio...

Original Swedish text: https://www.riksdagen.se/sv/dokument-och-lagar/dokument/sven...