Last week, we reported a list of the six largest mobile advertising networks—with the caveat that the data may not be correct. Well, indeed, it was a bit off, but for slightly different reasons than we thought. After rolling with the information from Nielsen (via Mobile Marketer), our sources contacted us to say that the list was incomplete. Two mobile ad networks were left off, and surprise, they were none other than Google (NSDQ: GOOG) and Yahoo (NSDQ: YHOO).

Perhaps, the list was intended to only compare the pure mobile ad networks, however, Microsoft (NSDQ: MSFT) and AOL (NYSE: TWX) were included. We asked Nielsen about the discrepancy. A spokesman said: “The difference is most likely due to measurement interval, but since we did not share this data publicly, I’ll respectfully decline commenting further.” Nielsen is clear about saying the information may not be valid because the ad networks are self-reporting the information and may all count their mobile web traffic differently. For that reason, the list is only a rough guide, at best (See more information in our previous story here).

Here’s the updated list in terms of monthly unique visitors:

1. Millennial: 45.6 million
2. Yahoo: 36.1 million
3. Google: 31.9 million
4. AOL/Platform-A’s Third Screen Media: 28.6 million
5. AdMob: 25.7 million
6. Microsoft’s MSN Ad Network: 25.4 million
7. Jumptap: 23.4 million
8. Quattro Wireless: 23 million