We had the same case; my wife had to travel out with a valid AP after 485 approval; but we did not get the 485 approval notice, and Boston INS would not stamp the passport without it (at least our approval case was not there in their computers the day we tried). One thing Boston INS folks did say was that the AP was good till we get the passport stamped. My wife has travelled out with that 'assurance' even though our lawyers were lot more conservative in their recommendation.
You are right, nobody outside US would know, if anything, there could be questions at the POE. Hopefully it will be uneventful for my wife's return. She is coming back next week, and I will post her experiences at the POE.
In the case of deferred inspection, will she get an I-94 or not?
I can see people are running into the issue of infopass appt date, in addition to getting the notice itself in hand.
PS: I got the approval notices few days after she travelled out, and I got my passport stamped and got my card in a month.
============ Update Sep 13th==========
My wife was able get back in at Boston POE on her AP on Spe 7th, no questions asked about 485 approval, etc. Stamp/485 all given like a regular AP. Other than the fact that she had sit nearly two hours in the secondary inspection room, even though there were no questions asked of her.
Then we got her passport stamped with the GC (I-551) stamp at Boston INS. The person who did her stamping asked a question why she did not stamp along with me, we mentioned my wife's travel; no other questions.
-vishuv