Musings about SPN

So, I've got to walk about a mile from the bus station to my apartment, and I got to thinkin'...
In IMToD, John drew the sign of Azazel to summon him (according to the WB website). Now, until Sin City, the boys didn't KNOW Stan YED's real name, and neither did we, really.
Now, considering in Home, John didn't know, or wasn't sure about things just yet, and in IMToD, he already knew not only that it was a demon, but it's name too, when do you think he figured it out? And why not tell the boys, or at least Dean (or Bobby or another one of his friends) about it?
Also, he must have suspected earlier, I mean, that's why he left Dean in the first place, right? So why not write about it in (either of ) his Journal(s), or at least leave Dean a note or something if he didn't want Sam to find out?
Which gets me to thinking, what else did he keep to himself? Does he know about Mary and the fact that everyone who knew her died?
And is it Thursday yet?