Dear,
I am not able to reproduce.
--8<---------------cut here---------------start------------->8---
# first to populate the store
guix time-machine --commit=91be384 \
-- build python-parso
# second to really build it
guix time-machine --commit=91be384 \
-- build python-parso --no-grafts --check
--8<---------------cut here---------------end--------------->8---
And I do not have any error. The substitute is available and the
rebuild is fine.
Could you provide the command-line that you used?
All the best,
simon
