Azerbaijan's 1992 mystery issue

Few stamp issues of Azerbaijan confuse me as much as the Other Overprints. Let me explain: one of the first stamp issues of independent Azerbaijan was a set of 5 surcharges on an unissued 15k stamp. The offending text of the stamp was obliterated by bars consisting of horizontal lines. However, the same set of surcharges was also available in the stamp trade with solid bars.
Azermarka, the Azeri philatelic bureau, isn't always helpful when it comes to these early issues, and Azermarka publications just ignore these "solid bar" surcharges altogether. That seems unwise, as they were accepted for postage in Azerbaijan itself, as we know thanks to Trevor Pateman:

Two stamps of the "solid bar" issue on cover from Baku to England. Sure, this is a dealer-inspired cover, and I believe Trevor even supplied the stamps and the envelope but a.) the stamps were accepted and b.) the letter went through the mail and reached its destination. QED. Note that this cover in no way proves that these stamps were available in Azerbaijan itself.

Trevor performed similar useful duties when it comes to those odd early imperforates:

Same caveats but same conclusion.

Coming back to the "solid bars" issue, I've found it to be an order of magnitude more scarce than the regular issue. The regular issue I have in sheets, for the solid bar issue, blocks of 4 is the best I can do and I'm quite pleased with those. I wonder if after so long, we'll ever find out the story behind these stamps...