Shadrich=Reed is just a guess. He is described as of very small stature, same as Reed, and there is the connection of Mad Mouse-Rat cook. Also, the cover is nonsense. Varys is missing since the purple wedding. That IT would have offered money to find S is true, but he doesn't say that. Lastly, I don't believe the knight of the laughing tree was Lyanna; imo it was rather Reed, bc he had been praying to the trees. Lyanna had to take the flowers, she was watching. So, imo it was Reed's m.o. again.
Actually, that is not true.
Varys only disappeared the night that Tyrion escaped, which is a good long while after the Purple Wedding. Varys was very much involved in the investigation, and the reward is offered almost immediately.
"I have taken Tyrion's squire into custody. His wife's maids as well. We shall see if they have anything to tell us. Ser Addam's gold cloaks are searching for the Stark girl, and Varys has offered a reward. The king's justice will be done." (ASOS, Jaime VII)
By the time Brienne encounters Shadrich she is half a week out of King's Landing after leaving shortly before Tywin was killed, so she even started out before Varys went into hiding. Shadrich's story is solid.
As for the Knight of the Laughing Tree, we know Lyanna was watching on the last day of the five-day tourney, not necessarily every single day from start to finish.
But late on the afternoon of that second day, as the shadows grew long, a mystery knight appeared in the lists.”
And why would Howland pray to the trees for justice against three squires if he could easily defeat three lesser knights in a tourney, even in a joust?
The lad was no knight, no more than any of his people. We sit a boat more often than a horse, and our hands are made for oars, not lances. Much as he wished to have his vengeance, he feared he would only make a fool of himself and shame his people.
One prayer to the old gods suddenly makes him a jouster skilled enough to unhorse three knights?
The Knight of the Laughing Tree had vanished. The king was wroth, and even sent his son the dragon prince to seek the man, but all they ever found was his painted shield, hanging abandoned in a tree. It was the dragon prince who won that tourney in the end." (ASOS, Bran II)
GRRM gives us a hint with another horse-mad girl of fourteen, currently bucking social convention in Dorne. Conveniently named for one of the two principal ladies in that tourney.
And Elia Sand, oldest of the four girls that Prince Oberyn had fathered on Ellaria, would cross the Sea of Dorne with Arianne. "As a lady, not a lance," her mother said firmly, but like all the Sand Snakes, Elia had her own mind. (...)
"And ladies do not joust," insisted Ser Garibald Shells, a far more serious and proper young man than his companion.
"I do. I'm Lady Lance." (TWOW, Arianne I)
My money is on Lyanna.
