"When you're happy and want to order the production quality you go back to JLC and click "reorder" and enter in 100/1k/whatever quantity. That way you know that the same data has been used to fab both boards."
JLC are too expensive for production work. Also, very limited ability to communicate in English. If you can't specify the job via the form on their website, it may come back "different". The other day I ordered 10 circuits and got back 10 panels of 10 circuits
Clearly I did something "wrong", but this would never happen in conventional PCB purchasing where you specify the panel layout, overall panel size, breakout tab detail (with photos), etc.
"Nobody is trying to assassinate your character"
Going back over somebody's old posts and digging up some other thread where that person got beaten up for something, is typical crappy social media behaviour. One sees it all over the place. Too many people with too much time on their hands... It's like you go on e.g. some snowboarding forum asking a question about snowboards, and a load of people dig up that you made a post in the off topic section, on brexit, and then beat you up, like a load of kids, in the snowboard section
(I don't snowboard, btw).
I don't think you and some others have even read my posts and the reasons for doing the BBT comparison. To say it yet again: it is to try to eliminate the risk of populating say 1000 boards (a 5 digit GBP figure) after a change of PCB manufacturer. I have been doing this routinely for many years.
Anyway, this question is clearly not going to be answered. I was wondering if there was a BBT machine which somehow cannot test more than one board. I suspect this time that this company subcontracts the BBT and doesn't want to get involved, so is pretending they don't understand. It is a not uncommon Chinese tactic. They know that you will never turn up at their door.