Hi Jonas,

However, the cardinality is given as "Optional, one or many." I'm not
sure exactly how to interpret this, as I noticed the spdx-tools fails
when converting from tag format to RDF if I don't have a Package
specified.

I would call this a bug in the SPDX tools. If you could log an issue in the
git repo and upload a tag/value file which reproduces the error, I'll take a
look at it (https://github.com/spdx/tools/issues).

Thanks for reporting the issues.

Gary