[mergen3107]

Some updates on my investigation.

1) I used showlog -f to see what is going on with the opened book. I was able to get something like this:

...
190113:223323 cvm[15492]: I ReaderInfoLog:BookInformation:book asin=f3203e96-c039-416b-aa47-9082f48637e3,file size=2200211,file last mod date=2018-11-18 18.56.26 -0500,content type=ebook,language=en/en,length=MobiPosition_ 1530687,access=2019-01-13 22.28.24 -0500,last read position=MobiSerializedPosition_ 968606 968607,isEncrypted=false,isSample=false,isNew=false,isTTSMetdataPresent=false,isTTSMetadataAllowed=true,fileExtn=mobi:
...

These length=MobiPosition_ 1530687 and last read position=MobiSerializedPosition_ 968606 968607 are definitely within my interest, however only the former appears in the cc.db . These values from showlog and cc.db match: 'length' and 'p_contentSize'; calculated 'last read position'/'length' and 'p_percentFinished' (about 63%).

2) @NiLuJe,
Thank you very much!
I tried your part of code from 'cover'extract' about extracting sqlite entries into variable and it works. So now I can tweak my needs of fetching these pieces of data from the last opened book. Particularly I only need p_contentSize, p_percentFinished types of data.

One problem I found though is that cc.db seems to be updated upon each book close, not every page turn. So now I have to think about how to properly determine current position to redraw it.

3) I used KindleUnpack plugin in Calibre to see mobi7 and mobi8 (azw3) files' contents.
For mobi7 toc.ncx file easily shows file position of each TOC entry:

...
<navMap>
    <navPoint id="np_1" playOrder="1">
    <navLabel>
    <text>Title Page</text>
    </navLabel>
    <content src="book.html#filepos241"/>
    </navPoint>
    <navPoint id="np_2" playOrder="2">
    <navLabel>
    <text>Copyright</text>
    </navLabel>
    <content src="book.html#filepos816"/>
    </navPoint>
    <navPoint id="np_3" playOrder="3">
...

As for mobi8, however, it is a little more tricky! toc.ncx does not reveal entries' position, but only tocref### references. Surprisingly for me, mobi8 files resemble epub files a lot, which also rely only on xhtml content size.
However, %book/Text/ folder contains separate files, each of which represents just another TOC entry (but it doesn't differentiate of which level).

So I am thinking about two things:
1) I should give up on different TOC level indications on progress bar;
2) I can calculate very rough position of these TOC entries based on ... cumulative file sizes with respect to total file size of this folder I tried it manually by hand on Victor Hugo's 'Les Miserables' (about 2500 print pages) and it works within +/- 3%

I'll try to write a little PC script (when I find enough free time) to pre-process mobi7 and mobi8 files to extract TOC entries' positions.