For Spain, that's indeed too Early. About two months in advance it'll be available, sometimes even less. 

Euskotren (Bilbao-San Sevastian-Hendaye) doesn't even share it's timetables with the world, but there are very frequent trains in between them. 

Yes you are too early. RENFE usually publishes schedules 3 months before but often it’s later than that.

However you can check the current schedules and it shouldn’t change much until October.

Thanks for the information, Brendan. I have more confidence now to push through with my plans. I was really apprehensive to book flights due to uncertainty of train schedules. My plan B was just to do Paris-Amsterdam-Berlin since they already have train schedules available for October/November.

Thanks for the information, Thibcabe. I have more confidence now to push through with my plans. I was really apprehensive to book flights due to uncertainty of train schedules. My plan B was supposed to be just to do Paris-Amsterdam-Berlin since they already have train schedules available for October/November.

Yeah, don't worry about that. As @thibcabe just said, just choose a random day e.g. next week and you'll see what to expect of train service for the end of 2023 . That goes for almost all train companies in Europe.

And even if there would be line closures because of works, there's alwyas gonna be rail replacement buses or diverted trains, or other routes to reach your destination.