@itonewbie   "if the return was filed before the extended due date, the SOL will run based on the actual filing date rather than Oct 15."

I'm not so sure of that.  IRM just says "Three years after the due date of the return, or three years after the return was actually filed, whichever is later."  That doesn't make sense for returns filed in November, though.  But I always have to look it up.  There's sometimes a question about whether the mailbox rule applies to October 15 returns.  I think it does, but not to refund claims using the "two years since paid" date.