There's a couple more interesting pages on Ed Fries' site:https://edfries.wordpress.com/2017/10/23/finding-the-first-videogame-rom/https://edfries.wordpress.com/2017/03/22/chasing-the-first-arcade-easter-egg/
According to a forum post in 2013 by Stiletto at https://forums.arcade-museum.com/threads/old-rom-chips-need-replacing.177683/
the rom in the Gran Trak 10 is a Mostek MK28000 PROM:
Sometimes you can't figure out how things work unless you build a model. I couldn't quite see how the horizontal counter system worked in Lemans.
The manual lays it out, but that seems confusing.
So let's take the schematic and make a logisim model:
and what you see is that 512H isn't actually 512H but represents more of the "right half of the screen" since it gets set after the 0x1c2 clock and the counter gets reset but leaving the 512H bit making 0x200.
(In other words, the counter jumps from 0x1c2 to 0x200).
Once it hits 0x3c2 then it gets reset again back to 0x000, and then does HSYNC for 32 clocks.
This explains why the 7th row byte disappears in the racetrack. 512/64 = 8 for 8 bytes, but 0x1c2 / 64 = 7.03 so it jumps from 0x1c2 to 0x200 which skips that seventh byte.