The title of this summary blog post is grossly misleading. (To the point where I suspect it of being an AI hallucination, thanks to its use of ChatGPT's distinctive formatting style of bulleted list with Capitalized Colon-Delimited Headers:.)

As the linked PDF explains, this is not a change to the postmark date system. It's an acknowledgement that the date on the postmark may not be the date that you dropped the letter into a (possibly unattended) mailbox. This has always been true, because the stamping is not done until USPS actually processes the letter. USPS has no knowledge of when the letter physically "entered USPS custody" by being dropped in the mailbox, so the postmark has never accurately reflected that instant.

This rule does not change when postmarks are applied, and it doesn't change how any other parties make decisions based on postmarks. It merely documents the postmarking process that has existed basically forever.