Just a sidenote: Since this is the second possession of this particular extra period, B has probably already put 7 or 8 points on the board. So, after the blocked PAT, there is a good chance that there will be no other period to carry over to.
The way I read the post was that that we are tied going into the 2nd extra period. Team A scores at TD to take the lead. The extra point is blocked by B. Team B is behind now by 6 points and will now get the ball for their possession series of the 2nd extra period.