1 - nice spot on the top car manufacture being linked to the middle one in the picture i provided - that's actually the games pre-defined/premade number 4 recipe with that issue (i never thought to double check the game's recipes), but after removing that link it didn't change anything anyway, so it wasn't that
2 - that recipe you nicely portrayed is exactly the pre-defined recipe number 3, the other one that i said for me only goes to like 80% to 90% and still doesn't max out, even with 2 sales squares. the other thing is though that even the 50% utilization recipe 4 still has that 1 sales square of only 60% utilization, you can see both that and it showing there isn't enough supply for the square in the image. so it can take more and doesn't seem to be at fault
3 - and i know the retail sales units aren't being fully utilized, i highlighted it to show my issue wasn't a retail throughput issue, as shown in the image both the purchase and sales are underutilized so it's not a retail side thing
so still smh at what's going on : P
and you might still think it could be the single sales square, but i've seen the utilization bar on a sales square go to almost full 90%+ when it's maxed, which isn't showing in this instance. definitely room to take on more. if the sales square is only 60% with factory output 50%, it stands to reason that if both supply and demand is adequate that both have room to grow by a half (60% to 90% sales uti and 50% to 75% factory output) no? or similar if it isn't fully 1:1
to recap: massively more demand in store than supply, but retail both input and output has plenty of room for much more supply, factory input/materials has way more supply than demand, and factory sale square is only 60% utilized - yet factory output is only 50% to 60%
P.S i also only have cars for that subsidiary so i don't need retail space for anything else, not to mention 3 floors is indeed required for majority market share in this large 4M pop city for the large cars, but yeah unlike most other things (i have 2 floor setups for compact camera and notebook computer for example)
but good to know "3 shops will get you higher market share once you got competition on same product" although i usually finish scenario's in 5 years at most each time, so competition (even own subsidiary/AI) don't get much done cause they move so slowly : P (and my squares especially slower manufacture ones don't get time to level, only mainly get levels from COO/AI expertise) but will keep in mind when finished with the scenario's!
Edit: i wasn't kidding about needing so much space for cars - onlyy 3 years in and here's an image of 2 auto stores, with 3 floors and 6 sales squares each floor (total 18 per store), with the 1 store shown all around level 7, the second all around level 4, with there still being a slight supply gap and only 50% total market share : P
35 sales square on average level 5 or 6 (with the last square being for advertising on a single floor of a single store) - big cars in big cities for big $ are no joke
https://imgur.com/a/khj2eKW
that actually also nicely shows full sales square utilization