

In general, I disable the ability of getting a ‘read receipt’ if at all possible. In the case of some rare platforms that don’t allow this; I also warn people that "Seeing a ‘read receipt’ indicator does not mean I was available to reply.
In general; people who hang on to this little indicator are also committing a larger social faux pas, and you should { [(yellow/red) flag] / address / handle } it accordingly based on your relationship to that person, your goals and the situation.
Whether that means ‘calling them out’ or kindly explaining what it actually means or explaining your approach to communications; the behavior of expecting something to happen on the receipt of a read receipt needs to be discouraged in my personal opinion.
This is absolutely not true; it’s absolutely possible and even suspected that individual game carts themselves are signed with unique serial IDs or even full certificates or cryptographic signatures.
I think it’s more likely the previous owner did dump the cart on to a MIG Switch or similar ROM cart. While the NS1 cannot tell the difference; it can still be updated to do so.
I think it’s likely that in order to play titles online; your Switch 1 has to get the Cart Serial number from the cart and package it all up nicely and sign it neatly with the certificate from the system. So if said Nintendo Switch 1 already transferred that title out to a Switch 2, then there would be a record on file with Nintendo saying “NS1 with Serial XYZ transferred Title cart ABC with serial DEF to Switch 2 with serial GHI”. Then when you put that cart into a different Switch 2 it notices and informs Nintendo of the new title and cart serial…which then immediately picks up on the change of ownership.
That might not raise red flags if you handed the cart over to your friend next door; but it certainly might raise red flags if you air-mailed the cart over to your buddy a few countries over.