[rglullis]

So, no. None of your examples are equivalent to OOXML. The implementations were first opened up and then standardized.

OOXML was the other way around: Microsoft had a standard and tried to enshrine into a standard and force others to waste time and resources to be compatible.

[pjmlp]

Only if you ignore what was standardised in PDF form and only later made available on existing implementations.

That is why I explicitly made references to specific versions as turning points, as I expected the usual FOSS advocacy replies.