FWIW, the weather forecasting computer model had just been changed and it actually was right, but they used a different model, which, obviously was wrong. There are 3 in common use, and you've got a good chance of being right when they all agree, but these didn't, and they chose the one that happened to be wrong...it was right for most of New England, though! Worchester, MA got 33.5" and set an all-time record for one storm - there were places that really did get hammered. I'm not sure what I officially had on the ground, but it looked like a bit over a foot. Enough to be a pain. A couple of miles, or a few hundred feet of elevation change can make a huge difference in a coastal storm around here.
Depending on the flange you choose, most of them have long slots for the hold-down bolts. THe holes in the toilet are also a little sloppy so that you can still make them work when you've slid the bolts and the toilet forward a bit. As long as the toilet outlet is still over the hole in the toilet flange, it can be off-center and still work fine...the toilet's outlet ID is in the order of a bit over 2", and the ID of the flange is at least 3", so you have some room to make it work off-centered, at least a bit. Just remember, when using wax, you can't actually slide the toilet, so you must preposition the bolts and set the toilet down straight to compress the wax and make the seal.