Missing Episode: His A-Team video game review was taken down due to copyright infringement (more specifically, a parody of the A-Team intro with the original theme music left in), but can now be found here, albeit without said intro parody.
His extras website (extras.ashens.com) used to lead to Stuart's page on the now-defunct video sharing site Revver. The videos formerly hosted there eventually were reuploaded to this channel by a fan who managed to save them.
To an extent, The Proxy could count as a trace of this. Each of the descriptions link to its Facebook, Twitter, and Wikipedia pages. However, the Wikipedia page has since been deleted.
Schedule Slip: Ashen's Tech Dump Episode 4 was released seven months after the previous one.
Also, as of this writing (May 17, 2014), he has yet to do a full review of either the Xbox One ("What's in the box" video released on November 22, 2013) or the PlayStation 4 ("What's in the box" released on November 30, 2013). In the description of the latter video, he says "I'm going to have to get a good look at both before I can really talk about either in depth".
What Could Have Been: Nintendo of America asked him to make a video for them, but he refused because they wanted full copyright without offering payment.