[AcidWeb]

OK. Finished my tests.

There is no way to remove Personal tag without injecting fake ASIN.
So there is no problem with the script - It is working correctly.

Summing up the situation with hybrid MOBIs. There are two scenarios.
A - There is fake ASIN number + EBOK tag
B - There is only EBOK tag

If file A will be uploaded by Calibre.
No Personal tag.
HQ cover will be automatically side-loaded to Kindle cache.

If file A will be uploaded manually.
No Personal tag.
No cover at all. Kindle will try to load it from cache - and fail.

If file B will be uploaded by Calibre.
Fake ASIN will be injected by Calibre. But it will only edit first MOBI7 header.
Personal tag. Due to lack of ASIN in MOBI8 header.
HQ cover will be automatically side-loaded to Kindle cache. But it will not work as MOBI8 header don't have ASIN.

If file B will be uploaded manually.
Personal tag.
Kindle will display LQ cover from book file.

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So it is lose-lose situation. File A work only correctly with Calibre. And file B will always have LQ cover and Personal tag.

Split files are simply better. Because you can make MOBI8 only file. And only change 501 to EBOK. Then this file will work fully correctly when uploaded by Calibre and still have cover when uploaded manually.

In this state it looks more like Calibre need a patch to support hybrid MOBI.