What I linked to is an official news release from the ISU. (As opposed to a news "article" from a third party, which would be a different kettle of fish.)
I find it quite implausible that the ISU officially has publicized the guarantee for at least the past three seasons -- if such a guarantee were (supposedly) not really in effect.
YMMV.
(In this thread, I linked to only the 2016-17 ISU news release, but in previous GS posts, I had linked to the corresponding ISU news releases from 2015-16 and 2014-15.
And yes, I am well aware that the announcements in those same years did not mention the guarantee. Nor did the announcements say that there was no guarantee.)
Fair point that it's been there for multiple years, though there are other contradictions in the news release compared to the official announcement. The news release says top 12 in pairs and dance are guaranteed two spots, the announcement says top ten, so it might be possible that there was a mistake.