Google Alert / link: operator

[plasma]

We all know, that the link: operator doesn't reflect the real backlinks and even if it would, the algo is far complexer than the set of backlinks. However it can be interesting to monitor.

I monitor the backlinks of several sites with [google.com...]
Yesterday and the day before I got several alerts of most of my sites for new backlinks.
One of my sites didn't get a backlink update, although I added many links long ago.

However it was that site, that didn't show updated backlinks that got the highest boost in the SERPs.
It is #1 now for many keywords I target that where 5-6 before and even for many keywords I didn't intentionally target.

The sites that got a backlink update, didn't change much in the serps.

I thought that nowadays the algo takes backlinks into account immediately when it finds them. But why does a site that got new backlinks a long time ago _now_ gets a boost in ranking that other sites got a "link:" update?