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Due to my travel at work, I have to travel through a number of ports of entry.... so much so that both my AP documents (one expired nearly a year ago) were and are beyond full of stamps indef stamps. Each port of entry will follow the procedure that 485/Waiter outlined, some with or without the plastic envelop

It is the standard procedure.
There are some port-of-entries in Canada (and this changes periodically), that do not carry out this lengthy procedure if you have been in Canada less than 24 hours. Upon asking the question to the "Port of Entry Officer" he responded by saying that this is determined at the discretion of the "Port of Entry Manager".
One port of entry did not even take me to the room, they just stamped the passport and did all the procedure right there on the desk (probably because I was the last one off the aircraft with a broken foot on crutches, and she did not want me to walk to the room

Basically, if you have all your papers in order.... (1) Passport, (2) AP, (3) EAD Card (sometimes), (4) I-94 completed, (5) Customs document completed and (6) I-485 receipt notice (rarely - but just in case) you are all set, assuming you are not a wanted criminal in the US

This is just my experience of having about 27 entry stamps on the first AP document and 21 on the second one yet.