You confirm my guesses, unfortunately. For the sake of the OCD-ish part of me, I may just turn off the saving to clippings so I don't feel like I'm losing stuff when using other devices.
After all, as long as the documents stay in the cloud, everything's available.
I'd tinker around with the mbp1 sidecar files, but I think someone with more experience with hacking Kindles would have better luck. I'm new to the platfrom (from a hacking perspective) so I'm quite clueless!