This interests me also.
It's my impression, from both the license-list explanation
and the actual list, that SPDX casts a broader net than
either OSI or FSF. Substantial compliance is sufficient.
I also note:
The SPDX Legal Team endeavors to explain its reasoning,
analysis, and conclusions
https://github.com/spdx/license-list-XML/issues/689#issuecomment-423262092
(about a non-open-source BSD variant):
discussed on Sept 20 call: as per the license inclusion guidelines at
> https://spdx.org/spdx-license-list/license-list-overview : "...any
> license that is a candidate for inclusion
