If your data format is so complicated that all commonly used implementations are not compliant with your spec, maybe it's a problem with the data-format.

Every single implementation people actually use seems to be a messy mix of yaml 1.1 and 1.2....

Maybe if the yaml project wants to consider this fixed, they should have written some correct reference parsers themselves for any languages in need, and encouraged their use.

I noted this in reply to the comment above, but: the YAML 1.2 spec doesn't actually mandate that parsers use the Core Schema. They left it as a recommendation. So I don't consider it to be "fixed" at all.