I've just signed Enzo Fernandez who is labelled as an "Extra non-EU player who cannt be registered until next season, or until another non-EU player is sold"
I have then sold Dario Osorio from my U20s who is down as a "non-EU player who occupies a non-Eu slot"
Even after selling Dario Osorio Enzo Fernandez does not become available for registration
I have uploaded my save files, Gethin Bradnam - Parthenope (v02) is from before the sale and Gethin Bradnam - Parthenope non-EU is from after