If my memory serves me right they didn't have transfer windows in those days.Also if a club did not want to release a player for international duty they did not have to.Not all things change for the better.
Also for your info I don't think there was an offside rule in those days as John Willy Parker of Everton fame would tell you if he is still around.
Even the end of a contract didn’t give players the option to move. Clubs held on tonplayers regidtrations which prevented them from moving, so if a club wanted to keep a player, they had an option. Play for us, or you won’t play anywhere.
Then came the Bosnan ruling from the high court and players the had the right to move at the end of their contract if they do wished.
Unfortunately for Bosnan himself. Although he won his case, it took so long to achieve, his footy career was pretty much over.
Modern day players hero.
He done as much for players as Jimmy Hill did, to abolish the £10 per week maximum wage 😳