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The transfer window is still open, and because both coaches are experienced, they will know whether or not to sign fresh players for the following season after selling some of them to other clubs. Teams who sell players do so due of the manager's decision; if those players cannot fit into the pattern of football they want to play, they easily release them and use the ones that are available, or better yet, look for better replacements for them. If they've been doing well even after selling some players, they should be able to do the same when the regular season begins.
The problem is not about regenerating players every season on a regular basis, but that some teams always have difficulty realizing their coach's wishes to recruit the players they are targeting. I believe Pochettino, Ten Hag, Klopp, Arteta and Pep Guardiola have a roster that they are looking at, but that realization may be too difficult because a lot of players have been up-priced by their owning teams.
Coaches will make adjustments based on their needs and plans, that includes who they need and who they don't. Chelsea is the team that has been the most aggressive in recruiting new players, they have also sold the most players who are not included in Pochettino's plans for next season.
I'm not too sure about Chelsea progress next season because I think they will struggle relatively when they have to face strong teams in the games they play. So far, I'm more interested in the developments that are happening at Liverpool because slowly, Kloop is able to make the quality of the squad more well-organized for their performances in pre-season matches. Even nunez is more confident that he can perform more optimally next season.
Even if you look at the players that the top coaches are after in the EPL, of course they can succeed in recruiting them if they are supported by the large budget that is given to them to recruit players in this transfer window. So far, only Newcastle United have looked aggressive enough in placing a lot of players in order to strengthen themselves in the EPL or Ucl next season. So for Manchester United they are still continuing to recruit in this transfer window and Erik Ten Hag has managed to recruit Hojlund recently. Manchester city is still active in recruiting players in this transfer window, they lost several of their core players in this transfer window.