AFAIK they haven't. The way they score [1] seems to suggest that they might be missing out on companies like https://gorickshaw.com and enterprise focused companies because these company might not perform well on mobile downloads, inbound links, twitter followers, facebook followers and linkedin followers (the six metrics they track and score on).

I personally feel that inbound links, twitter + facebook + linkedin followers don't add all that much to painting a complete picture of the companies that might not be in the "social" space but I feel that if they keep at it long enough and keep iterating, they will eventually figure out how to be less wrong (Even most top VC firms aren't able to consistently pick only winners).

[1] https://mattermark.com/mattermark-score/