@mgiven recently a 1.1.0 version was tagged, and includes the concept of collections of recordings.
The Python sigmf library recently got its own repo.
https://github.com/gnuradio/sigmf-python
And for those doing it on C++,
https://github.com/deepsig/libsigmf/
SigMF: The Signal Metadata Format https://www.gnuradio.org/grcon/grcon17/presentations/sigmf/Ben-Hilburn-SigMF.pdf
PySDR: A Guide to SDR and DSP using Python (Section 11: 11. IQ Files and SigMF)
https://pysdr.org/content/iq_files.html