That is interesting. My wife's only questions when traveling with her expired GC and EL was when traveling from PEK to DTW via Delta. The local check-in clerk was not familiar with the EL and asked to keep it. Luckily we had a few copies with us, and gave her one of those, and my wife was allowed to proceed. This is one of the reasons I always recommend those traveling on the EL make a few copies although I have not heard of anyone else being asked to hand over the letter at check-in. It is interesting, the CBP link you provided referenced the 18 month EL, back in March of 2021, I guess this needs to be updated.
To the OP, using the US CBP Carrier guide is always a good idea. We downloaded a copy of the PDF on our phones just in case. Airlines bringing folks to the US should be following this to a tee.
B. U.S. RESIDENTS — must provide one of the following:
• Permanent Resident Card, Form I-551
• Expired Conditional Resident Card, Form I-551 accompanied by Form I-797, Notice of Action indicating the card validity is extended
https://www.cbp.gov/sites/default/files/assets/documents/2019-Mar/2019 Carrier Information Guide - ENGLISH.pdf