We have been told guys that next league season will be so5 only so only guys/girls that will be in the league must be playing the so5 version of the game right? i'm not that technic but how can you tell if someone uploads a horse from starters orders earlier version?

I believe that the file itself when exported will be enough to tell what starters orders game it was played on.

Ok thanks but when i look at my exported horse files it just gives name age and region and when i look in properties at the file apart from my name and computer and owner it doesn't give any insight on what game or anything it comes from.

It tells u when u load up a horse i think

The horse file just won't be recognised. With the changes to stamina, jockey instructions and the like the new horse files will be different.