If you mean the phenomenon of a score-reel-like dummy zero, start with Williams Army Navy
https://www.ipdb.org/machine.cgi?id=91
and read the notes. But that's from the era where bulbs behind the backglass dominated. In the early 1960s, all the pinball games used score reels and scored in single points. Then phony zeroes reappeared; Bally was a big proponent. There are a couple complicating factors in analyzing scoring styles of the sixties, though: add-a-ball games got phony zeroes ahead of their replay counterparts, and rifle games almost always had at least phony zero throughout this time range.
.................David Marston

Williams "Army Navy" would be my guess as well. In the early fifties, they ran off about a half dozen games with score reels. They had only three active reels, and the rest of the digits were dummy zeroes.
Oddly, Williams reverted back to a game with bulb scoring in the early sixties, called "Space Ship". By this time, score reels were standard equipment in all pinballs. I believe "Space Ship" was the last pinball with lamp scoring. I believe you may be correct about "King Rex".
The domestic replay version "King Tut", had four digit scoring, with four active score reels.
Bally "On Beam", which preceded it, has five digit scoring, using five active score reels. I can't think of another game which has this.
"King Rex" was meant for export, and overseas operators were already hacking four digit games with a fifth dummy digit. Perhaps Bally caught on to this, and produced Rex with a factory installed dummy zero for the foreign market.

Primarily in the time frame before backboxes. Games in the early 30s had no backboxes so many playfields had score reels/counters and these were called totalizers. On IPDB, do a Quick Search using the word "totalizer" (no quotes) to see them.

Also, do a quick search on "dummy" (again, no quotes) and you will find 1934 Autobank has two dummy zeroes in its playfield totalizer.

Quick Search is your friend.