The transfer window closed on Tuesday night, it shutting with a slam at Deepdale as North End brought in Ali McCann and Josh Murphy moments before the deadline.
In McCann's case, the paperwork was received by the EFL with a matter of seconds remaining.
Clubs in the Championship are permitted to register up to 25 senior and loan players in their squad.
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Any player aged 21 and over on January 1 this year counts as senior and has to be registered.
In PNE's case, McCann turned 21 last December and falls into the senior player category.
Players under the age of 21 don't have to be registered and clubs can have an unlimited number of them available for selection.
The 25-man squads only cover league games, with players who miss out still able to play in the Carabao Cup and FA Cup.
Spaces can be left free and filled as the season goes on, for example in the event of a player coming back from injury or being signed as a free agent.
Meanwhile, a transfer done by Barnsley late on Tuesday was only announced on Thursday.
The Tykes signed left-back Remy Vita on loan from Bayern Munich,
However, paperwork and registration issue meant his move could only be rubber-stamped and announced nearly 48 hours later.
Elsewhere in the Championship, clubs are keeping an eye on the free agent market if they have any room left in their squads.
Some well-known players without a club at the moment include Jack Wilshere, Andre Wisdom, Hal Robson-Kanu, Smaba Sow, Jordan Ibe and Mo Besic.
Derby County, who have been working under the restrictions of an embargo due to financial issues, have lost defender Craig Forsyth for the next three games.
He has been hit with a suspension by the FA for violent conduct during the 1-1 draw with Nottingham Forest last Saturday.
The incident was not spotted by the referee during the game but the FA charged him retrospectively after viewing video evidence.
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