There are no corroborating accounts. The Scott Forbes story is what it is - which isn't much.
In a subsequent "interview", he didn't substantiate the original CT story, he admitted that he didn't know anything about floors other than the few floors that were occupied by the company he worked for (there goes the "50 stories" claim); he had absolutely no basis except for his own (misinformed) speculation about what it actually meant to have a "power down" - i.e. the nonsense about security cameras and locks being inoperable is BS; he had no way of knowing anything about most of the things the CTers think his story "proved"; the timing changed from all weekend to 26 hours; he could not provide any details whatsoever about the alleged email he read about the alleged "power down", not a name of who it was from or even the department or group that it allegedly came from; he couldn't provide any description of the people he purportedly saw in the building that were somehow "suspicious"; he didn't provide a single name as a potential corroborating source even though he says "lots of people" knew about it and could/would corroborate his story.
Basically, his subsequent "interview", assuming it's legitimate although I'm not convinced yet that it is, is far less damning than the initial report attributed to him by CTers, but it is still far from satisfactory and it is still far from proof of anything since he gives no details that matter, offers no descriptions, wasn't in a position to know most of the things CTers claim his statement proves, wasn't in a position to observe most of the things CTers claim his statement proves, doesn't say where he was located in comparison to the mystery workers, (and come on, if they were planting explosives, they weren't doing it in the occupied office space - duh - so how and where did he see these mystery people while he was, supposedly, working away in his office? Etc.
The whole thing smacks of conspiranoid nonsense.
And there are zero, zilch, zip, nada, reports of any such "powerdown" in the other tower, by the way. Not a one. Same for WTC7.
Moreover, had the World Trade Center actually been effectively shut down for the weekend, or even for a day, it would have been big news, because the towers never shut down entirely. Never. Yet nary a peep about such an unprecedented and unheard of event was ever noted or reported upon? Sure.