The request on single sided printing may have been driven by the information page added by some tax software vendors.
I noticed that the number at the bottom of my pdf Form 540 (3101183) differs from the number on the form in the hardcopy tax booklet (3101187). Those numbers also change from page to page. My form prints out a little smaller with larger margins around the page. I wonder if that is an additional challenge for their scanner.
I believe the filing date should be the date of the postmark. It’s possible they scan returns that are not late as an easier method.
My returns were placed in the regular mail without proof of delivery and it was nice to be able to verify their receipt online. That included use of the Refund Status link on the IRS site which I used for the first time.