I think it happened pretty recently. I don't know when but my site now has "proper" TBPR displaying. I did make some small footer fixes recently that may have put me in the gutter previously but the PR I am seeing is new to me.
There was some buzz about a limited TBPR update a few weeks ago, but my sites all stayed the same.
I try not to care/worry about it. TBPR is not really a KPI for me, but some people stare themselves blind looking at it - so for (as an example) link exchange purposes it has a lot of value since I can hand out useless links from even less useful domains and get great links to my money-making sites in return.