The deployment schedule is not quite that simple. If you open the
'Included in' section of the breaking commit, you can see it was included
in wmf/1.26wmf21. According to
https://www.mediawiki.org/wiki/MediaWiki_1.26/Roadmap that was deployed
to
mediawiki.org,
zero.wikimedia.org and some test wikis on the 1st, most
wikis on the 2nd, and then only Wikipedias on the 3rd.
Indeed. I could've been more precise here.
Thanks again Alex,
–Sam