Having associated my Math.SE account to meta.SO (to post this), I got the association bonus +100 on both sites. The
reputation tab in my profile confirms this. But the drop-down activity summary, shown when hovering over my user name, says it's +90.
Looks like a bug. I thought of posting this on meta.SO, but there the amount is shown as +100 in both places. Could be a Math.SE-specific bug for all I know.
Clarification: "drop-down activity summary" with +90 is shown when hovering over my user name here:
I am unaware of a more official name for it.