Your reply makes little sense to me tbh. If you have a deadline day to register new signings or other players then it is impossible to register any new player after the deadline, be it outside or within the club.
Be it in baseball, basketball, rugby, soccer, no one can register players for any competition if they are not registered before the deadline day, to which these ''draftees'' fall into this category.
Because if you can register players even after the deadline then there is no point in having a deadline at all?