Seems as though the infection spread further and goes back farther than I had originally thought. But this does help to close in on the issue. I had brewed 2 ESBs to do a side-by-side comparison on two yeasts. The one that happened to be in the fermenter that had housed the infected batches was very slow to start fermenting and had lots of phenols once bottled. It seemed to have better carbonation than the other version as well. I had originally thought that the phenols were from a stressed fermentation since the yeast pitch came from a local brew-pub, was from an Imperial IPA, and was mostly hop sludge. Turns out, after 4 months at room temp, we have gushers again. Looks as though the gusher bacteria took hold while waiting for the yeast to grow and work.
I also found one last bottle of Free Bag O Malt Mild, the first brew from the conical which happened to be in the fridge since bottling back in September 2011. Gusher. I think my hunch of the bacteria inhabiting the used conical is more than a hunch. The second batch in that fermenter was only in it for 1 week, and it had some fairly powerful bubbling when I popped the last one of those this weekend too, never gushed though. So first batch in conical, gusher. Second, over carbed. Third, gusher. Fourth and the one from my other fermenter that got a re-pitch form conical #3 batch, gushers. Another fermenter repitched, gusher (5th from conical seems to be okay even though it has the same repitch as the other fermenter, yet it is a 10.6% beer). Yet another batch from a different fermenter that had housed 2 infected repitched batches, gusher.
Needless to say, I pulled the American Blonde that was fermented in that Better Bottle from the fridge to leave in the garage for a few weeks at 70+ degrees to see if it gushes as well.