If a player played for Clan X in CL 9 and moved to clan Y in CL 10, then they can not represent Clan X in CL 11. This rule is meant to stop free movement of players and restrict the advantages gained via allied clans (For ex - FakeNamePlayer for Masters/Apex, Lynx/101st, Masters/Apprentice, GG/GGr etc). The only exception to this rule is if Clan X drops out of the Clan League.
You kinda butchered the rule, lol. Ignoring the exception, Masters hasn't played since CL10, so even if it wasn't there, the rule would not apply.