I just want to confirm something.
I would say in old nav versions if they key didnt exist it simply used to fail. It seems like, now it searches for best ocurrence of index fields for the given setcurrentkey:https://docs.microsoft.com/en-us/dynamics365/business-central/dev-itpro/developer/methods-auto/record/record-setcurrentkey-method
Strange also, I tried random fields not included in any key and it always returns "true" for:
[Ok := ] Record.SetCurrentKey(Field1: Any [, Field2: Any,...])
I even tried a calcsums and it worked.