LOL... No one "wiped all previous posts from the internet", that really doesn't happen when it is from multiple sources all over the globe, and especially not for information like this.
The reason you can't find references to it, is there never was a promise or guarantee of 2 years of updates... it was always stated by Moto that there would be "quick updates" and Google's Motorola had agreed in principle to the 18-24 months of updates for most devices. Many people and article writers put this two together and that somehow became a promise or guarantee it would occur, and for a while Google's Motorola largely fulfilled that "promise" that didn't really exist.
But does that show that Moto/Lenovo never made a promise? Nope, but articles like
this one from over a year ago, almost begging Lenovo's Moto for a concrete update policy of some sort, imply there never was a promise or guarantee.
The end result here is Lenovo has failed to stand behind the products of the company (and philosophy) they purchased... Why? Because Lenovo has a history of not caring about anything but profits and company, regardless of the customer. Unfortunately, many people see Lenovo as still part of IBM so even with all the scandals surrounding them over the years and a general lack of respect for consumers, they thrive largely on the corporate/enterprise market.
TBH, I have no idea why Lenovo bought Moto, unless it was to take the brand name that has a loyal following and respect from users and critics combined, and slap it's name on every product it can churn out and sell, and milk the name dry for the profits it can get over a few years.