1965 barracuda spare tire cover question

OK, I measured the panel that came from a '65 and it is not quite 1/4" at only .221 I've never seen 1/4" hardboard (Masonite) at Home Depot or Lowes but it is usually available at a real lumber yard or even Menards. https://www.menards.com/main/buildi...ard-panel/1291185/p-1444431330429-c-13340.htm
Panel1.jpg

So this discussion got me curious enough that I checked my other cars and found the original panel in one '64 Barracuda to be different as well. Panel 2.jpg

The third '64 Barracuda is .221 material as well but I got it late in it's life and well worn so I don't know if that panel is original or not.
So I've got two Barracudas with the .221, one Barracuda with .165 and my '64 Valiant, with a larger trunk panel, at .131 thick. I'm guessing they cut them from whatever suitable material a supplier had available at the time. Maybe it is like the trunk divider with no rhyme or reason to which ones got the right side extension and which didn't. I got the '65 panel given to me in 1973 by a guy who bought the car new. The original owner of my car had spilled boat motor oil in the trunk and the panel, carpet and pad got soaked and ruined, so when the guys' '65 got in a fire at his shop he salvaged stuff from his low mileage car to put in a really high mileage replacement '65 with a nice body. So for many years my red Barracuda had a gold trunk carpet that smelled a bit of smoke!