>> Isn't releasing the details of the hardware design mandatory to qualify
>> as open source hardware [...]?

> I [...] no doubt will default to however Roberto wants to handle it.

Hasn't that been clarified a while ago already?

"At the end of this past year we started to consider the possibility of making our motherboard Open Source Hardware (OSH). After discussing the idea with the hardware producer, both sides agreed that this was a good idea. We announced this new challenge at the beginning of the year and now we think is the perfect time to clarify the implications of making the motherboard Open Source Hardware. [...] A complete and detailed explanation can be found on the OSHWA definition page, but simplifying it even further, we can say that OSH is hardware made in such a way that its design is publicly available. Not only that, the documentation provided to understand and reproduce the device should be friendly, in terms of allowing its edition and improvements. So a PDF file containing the schematics is not enough to describe a hardware device as open source hardware. To open source a hardware project, the complete set of CAD and description files should be provided, enabling for instance the edition of the circuits. Of course if any firmware is used to make the hardware work it should be also available as open source code."
https://www.powerpc-notebook.org/2016/10/about-open-source-hardware/

This sounds unambiguously clear to me.