The main difference between these two cards was the 10 was submitted by a bulk submitter, and the 8 was submitted as a one-off, or small lot. Hearing these explanations for the physical differences is comical. IMO, if your going to submit post '77 cards, submit 100's at a time, not 10.

What is the trick to correlating the psa cert number to the approximate year it was graded?

I see a 4 you are stating is 10+ years ago and a 237 is 2-3 years ago.

For some reason, all the ones with flips starting with 30,000,000, 50M, and 90M were all graded very long ago. At some point, they restarted with numbers closer to zero and continued on that path to current day. When I first started grading cards 5 years ago, they started with 20,000,000. They've graded about 1-1.5 million a year since then, so they're about to hit 30M again. Not sure what numbers they'll use once they hit 30M, because they've already used some of them.
You can tell the age of some based on whether the flips have the Grade Text and number on the same line (like VG-EX 4) or the 4 on a separate line. Ones with the grade number and text on the same line are older. Then they added the first edition hologram on the front, and then the "lighthouse" flip most recently. I am not sure there is an official list of which cert numbers were used when. But I bet a bunch of us could manufacture one.

Here are numbers from my submissions over the years:
May 2014: 22,822,017 (no hologram front)
April 2015: 23,522,338 (no hologram front)
June 2016: 25,848,903 (hologram flip, bar codes on back)
May 2017: 27,367,603 (lighthouse flip)
I submitted one in November that hasn't been graded yet, so I don't know what those cert numbers are.

Thanks for the info. Is there any place to go to see the history of PSA flips/gilders?