[...] nobody has played all the levels, there's not enough time in a lifetime to actually play / look at all the levels, they just know that's how many there are because that's what the code does ;-)
That makes sense. It's infinitely faster to understand what the code does than going through the 130 000 000 levels.
<MainMemory|Away> afaik the S&K cart's mapper always forwards addresses from $200000 onward to the locked on cart, so multiple S&Ks would just keep forwarding the request until it reaches the end of the chain
I'm quite impressed by the design of this lock-on feature. During those old times, people really took the time to test and fix the most exotic use cases.