Looking at the latest polls from New Hampshire they seem to mirror Iowa... so I'm curious if a "deep" reversal on Super Tuesday etc. has happened, i.e. did someone not in top two in either Iowa or New Hampshire eventually win the Democratic ticket?
According to fivethirtyeight it only happened once, in 1992, i.e. Bill Clinton won without winning either state, but...
the circumstances were unusual.
Iowa wasn’t really contested due to the “favorite son” candidacy of Iowa Sen. Tom Harkin, and Clinton lost the New Hampshire primary to Paul Tsongas, a former U.S. senator from Massachusetts. But Clinton still managed to outperform expectations there, which helped him on his way to the nomination.
According to the same source Biden claims he can repeat Bill Clinton's performance, on the strength of the minority vote in the southern states.
The BBC even has concise(ish) presentation of exactly who won what in these two states (among Democrats)...