As I see it,would every Club looking to get transfers in,really be aware of every Player in the World who is available.for them to make a bid for or apply for a loan,with a possible option to Buy later ????.
Occam's Razor is a line of reasoning that says the simplest answer is often correct,so if you apply that to some of the Players that have gone to other Clubs,perhaps we just did not know they were available , perhaps we are looking in different Countrys,different Leagues !.Club Scouts can not be everywhere,so the manager etc must have some specific ideas in mind of what he wants,and until he gets a Player who meets that criteria,AND is available then the Club will keep on searching,but without a doubt they will be searching for those that have been identified as targets for transfer.
It was interesting to read that Bournemouth are even checking Players Social Media,to see if they might fit into their transfer plans.