Does Yahoo! have a known extended sandbox period?

[JS_Harris]

I'm not referring to the time when a site is first launched and not indexed yet, I mean after 2 years, is there an extended sandbox?

I'm asking because of a noticeable pattern in search traffic to my sites. I'm used to seeing Yahoo! and Google account for 80% of my total search traffic with Google claiming roughly 75% of that.

I've just had a 3rd site pass the 2 year mark and like the two before it traffic from Yahoo! has spiked upwards fairly significantly at that point. Yahoo! and Google now account for 90%+ on these three sites with a 60/40 split in Google's favor. My younger sites don't receive the same benefit.

Just random coincidence or is there an extended sandbox period of some sort?