In Silence in the Library, River Song sent a messege to The Doctor. She told him to go to The Library, but it got to him earlier in his timeline, since it went to his 10th incarnation, way before he met her. Why did the message go the 10th Doctor? Was it supposed to go to his 11th (Matt Smith) or 12th (Peter Capaldi) incarnations?
With the recent episode there is actually an answer to this.
The message was supposed to be for Capaldi's incarnation.
The reason is because, spoilers if you haven't watched the latest one:
In the episode The Husbands of River Song at the very end The Doctor gives River Song the sonic screwdriver she will use in Silence in the Library. That means directly before that particular moment in her life she met the 12th Doctor, which would make sense as to say how he looks so young. She also has knowledge about stories regarding whether or not they will spend their last night at on Darillium and he responds by saying "Spoilers", but does reveal that one night is lasts twenty four years there.
The main reason it went to the 10th Doctor was because River Song's whole timeline with the Doctor was shaky to begin with.
Just to clarify River Song and The Doctor's always meet in strange order.
Best assumption is that Ten was in closer proximity, spacially and chrnologically, when she sent out the message. One could make the same guess when any message makes it to the Psychic paper, like that of George in Night Terrors, or even when someone phones the TARDIS, as in Winston Churchill in Victor of the Daleks.