Hello, Elle!
My take on 17d!
"I am" means the same as "this writer is".
"I" and "writer" being the setter.
The setter has persuaded me, but maybe you do not think so much of it.
Just the way it goes in puzzles, at times.
I do not know what possessive "s" means.
Getabird ran a very good race.
He kept them honest until the last 2 furlongs, then seemed to run out of puff.
One more horse today.
Apples Jade. I like her a lot.
Hope she runs well!