It's also possible that several witnesses read it here or elsewhere on the net. But the future will show if it is so. Last change was not as big a change as they like us to believe since 90 hours was based on 1000 hours a year and the 70 hours was just that 70x12=840 that was only about 13 hours less then the previous 90 and not 20 hours as they liked us to believe.
The last change (from 1000 hours to 840) also did away with what some could interpret as a measure of actually caring for the pioneers.
As you noted, the old goal was 90 hours per month. If you did that for 11 months, you'd have 990 hours, and you'd only need to get 10 hours in August to make your time. A lot of pioneers took full advantage of that, and took many weeks off in August (the traditional European vacation month).
With the change to an 840 hour year, the monthly goal was set to 12 months of 70 hours each. No more "vacation time".
Of course, if you happen to get 830 hours by July 31, you could still do your "vacation time".
But there is an important difference: pioneers get "credit" for working on certain "theocratic activites", like Kingdom Hall construction projects or Bethel temping. If you use that credit time, though, it only counts up to the "monthly goal".
In the past, a pioneer could work often on KH construction, get their credit to boost their hours to 90, and still have time to squeeze in a vacation.
Now, they can count a maximum of 70 hours in a month if they are using this credit - no more "Society sanctioned" vacation time in August.
Just one more small measure of the Society's desire to keep everybody running full bore on the hamster wheel.