Difference between Unattached and Expired in Scouting

[Ayrton Senna - Cmac]

Anyone know what the difference between unattached and expired is? 

I used to think Expired was players who's contracts ran out but they stayed at the club on a month to month basis, but when I look at all the expired players in my scouting range, almost all of them have no clubs at all. There is also far more players under the expired filter than there is on unattached. Here's the screenshots below. Any help greatly appreciated! 

EXPIRED FILTER, 1537 players: 

 

UNATTACHED FILTER, 319 Players: 

[DarJ]

Unattached players have no clubs while expired contract players can still have clubs so it’s normal to have more players with the expired contract filter