Why does Open Site Explorer list Twitter and Facebook links for one of my sites and not others

[4wheelparts]

One of my sites has the nofollow backlink listed for Facebook and Twitter while 2 other sites do not.  All 3 sites have had accounts for over a year.

Does the amount of interactivity with the social media profiles have to do with it?

I know it is a nofollow link but I was just curious as those profiles might help with the brand signal etc.

[Nemek]

I suppose even Facebook and Twitter don't get crawled deeply enough to get fully index by the SEOmoz bots. Profile pages that have more links pointing to them (even nofollow) have a larger chance of getting found by a robot.

[Dan-Petrovic]

OSE index is limited however it may be the case that your other site's links get indexed more thoroughly next time.

[Guest]

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