What is the correspondence between the bids-validator version number and the BIDS Specification version number?
Unfortunately there isn’t an explicit correspondence. Changes to the validator try to match what is current in the stable spec. The most sure fire way to tell what version of the spec that the validator is working from is to look at the commit dates on the validators repo for the version tag, and then cross reference it with what was current at the time in the spec repo.
Thank you for bringing this up, I’ll make an issue in the validator on how we can make this more clear moving forward.