Okay, so I guess it sort of makes sense that the events of Time's Arrow didn't take place in this time line, so Guinan wouldn't know Picard. But couldn't the writer's help us out a bit so that we, the viewers aren't confused? They could've had Picard, after beaming in and realizing he was going to talk to Guinan, call back to the ship and excitedly say, "I'm going to speak to an old friend, but I don't think she will remember me - we met in a past that we need to restore" or something. It wouldn't have to be a lengthy recap of Time's Arror, just a little something to acknowledge the convoluted time travel scenario set up in TNG.
But to go further down this time-travel rabbit hole, I thought the reason they went back to this point in time is that this was the moment where "one event" changed all of future history. So wouldn't that mean that everything prior to that event would be unaltered? How could Guinan's past on earth be different if the event that changes the future hasn't happened yet? Ugh. To quote Talledega Nights, "My head's all tied up like a pretzel. I got a pretzel in my head!“
Edit: just remembered another thing that bugged me - the "15" clue that Picard and Agnes figure out (possibly another Easter egg from the TNG episode "Clues"). They jump to the conclusion that it must be referring to the time the "event" happens - already a big assumption, but whatever - Agnes says "15 hours?" to which Picard says "not specific enough," and decides it must be referring to the 15th day of the month (three days from then). So that's another big assumption, but my question is, how is it that the date of 15th is more specific than 15 hours??? 15 hours is a smaller amount of time, therefore by definition, more specific than a date three days away! If the time altering event happens on the 15th, what time does it happen? Right at the stroke of midnight? Or is it at 11:59 pm, right before the date changes over to the 16th? Or 10 am? 4:20 in the afternoon? 7:36 and 32 seconds pm, precisely?