Thank you for the feedback.
Yes, these were more or less my suppositions too, althought regarding locations I still hoped that something could work being the text the same (I thought that offsets could be applied to the actual text deprived of any custom data).
If I manage to get the "association" part with the store to work (using the values you mention, of which I already read
here and
here) I think I could still give this a try with some inexpensive book of those I already own from the Play Store (Google).
If the PDOC tag is added back in the emailing process I think I'm stuck though, as I don't own a Kindle and I can't "send directly" to any such device.