What which part of the system can detect and see is absolutely relevant, because nintendo can't ban people for something, if they don't receive the info that its happening.
So lets take your example with the fuses, in theory they can detect it, because we know the boot loader checks it, but has any system module access to the fuses?
If I remember it correctly, mostly the bootloader and trustzone use the fuses directly, while the rest doesn't use them directly. So if I'm correct, then one of the components we know 100% what it does handles this, and we know for certain that its not send to Nintendo.
So there is a big difference between things the console can actually detect, and what Nintendo can detect about you as a company with its current firmware.
About people playing backups, I actually mentioned before, that they don't need to directly lead to a quick ban, as long as you are not connecting to the online services for usage with the game. I even used game XCIs via emulation in SXOS in the past, but always offline, and pretty much only to play games I preordered early. One of the switch consoles from my family even had a game NSP installed in the past and is still going online. That's why I said they can lead to a ban, in case ticket data gets send. One of the cases where ticket info is send, is during moments where the game connects to online servers, but its possible that there are other triggers where tickets might be synchronized. Its also easy to accidentally connect online in a game if people use a mixed nand, which is a big potential error source thats mitigated via emunand for people using backups.
The questionaire being limtied to yes and no questions helps a bit with the answers the users can answer, but it also has the potential, that smaller but important things are still not reported by the users, because they are not in it.
For example if somethings like tinfoil installed itself, the user would not put it in as them installeing NSPs. Even just installing their self dumped XCIs, or for some installing NSZ (or what it was) files can lead to the users reporting this as no, since they might not understand that its all the same. So the user will still only report it based on their level of knowledge, which is to be expected, but limits the ability of this data telling us that just CFW is problematic. It can tell us on the other side that some specific thigns might be problematic through, especially when combined with analysis of the system.
And Your point about lying only is importent if we expect the user to lie, but I never said they intentionally lie, I said that some answers might be wrong because of their lack of knowledge in some areas, which is not lying.
Also when a user is unsure about something, even just the way a question is asked can lead to different answer, which is why an eyewitness might sometimes report wrong info.
And about the ban proof, its easy to use sysdvr to proof I'm currently online in CFW and can go online in a game by just streaming it and using tesla overlays.
For the past on the other side, the evidence is not 100% water tight, since I might regularly use different switches, but its more likely I'm telling the truth as you mentioned.
For example based on the Fuse count and system error log I can also give good evidence about the likely timeframe in which I already use CFW, and that I never did a normal stock bootloader boot since then.
Also the newest entry in the error History under Settigns->Error History is a 2124-3001 from march 2020, before that there where regularly new entries, and not a single one after it.
Based on the play history its also possible to at least give move evidence that I used a switch a lot since then. I also have a public playlist with unlisted streams of splatoon from after the last error log, that where made using sysdvr, and probably also some local recordings, with some recordings probably also showing the FPS counter or somethings else from tesla.
