Thanks Pib. Very helpful, and a little unsettling.
OK, this has been covered in various posts, but based on reading this lengthy thread, this is my super-paranoid plan:
1. Send original and second request forms to PA via Registered Mail as per usual.
2. Email Manila with tracking #, advising scan available upon request*
3. Use a remailing service like the one the OP suggested https://www.letterstream.com/
to mail a scan of the 7162 regular first class mail through the U.S. Postal Service. There is another similar service I have used in the past that works well too. Ironically, it is much cheaper than even registered mail ????, and a log of all your mailings is readily available, and additional layer of proof.
4. Keep nose to the grindstone and ear to the wind with fingers crossed! ????
*I am sure that Manila is less than enthusiastic about receiving such emails, and can do nothing with the info, but is is just another layer for establishing compliance should the tish ever hit the fan.