I m a doubt, i had finished my first year, with a custom team, and when i arrived to october, november, and dec, I can´t contract any rider, and any trade between teams.
I only contract free rides or in last year contract, always said, you can´t contact with this rider until 15 oct.
You cannot buy riders you can only sign free agents.
It is not easy to see which riders are without contract or will not prolong their contract. You can use the search and set two filters (contract = free OR contract = ending). If you contact them it might happen that it says something like 'wait until 15 oct'. This is a bug or wrong translation as it should read like this: "This rider already signed a contract for the next year"
You should prolong the contracts of your riders before July and starting from July contact young riders and/or other riders. As far as I know, young riders need to be contacted before the 15th of october, else they will sign a contract for the after next season. I am not sure but I think I was able to contact normal riders after the 15th.
Glad I found this thread because I too was curious that I could not do any transfers. Of course the manual says you can. Imagine that something in a game not working the way the manual says.