There was a group of nobles.
They followed their Lord into battle, only for the Lord to die on the battlefield. The fief lacked an heir and was directly annexed by the superior Lord. However, the superior Lord refused to recognize the landed rights of this group of followers of the deceased Lord. Consequently, their lands were stripped away, leaving them with nothing but an empty noble title.
And there was a group of impostors.
What they were best at was forging their own noble identities, such as a bankrupt Honored Knight, a Baron's follower whose Lord had died, or a Viscount wrongfully deprived of his lands. In short, they possessed so-called noble statuses, fabricating all sorts of fallen backgrounds.
The state's vast territory and backward transportation made it very difficult for ordinary nobles to verify these impostors upon encounter.