There are, amazingly, 13:
the original 4 from 1969
the 2 originally approved for the Holy Year of 1975
the 3 originally approved for Children’s Masses (the most problematic of the bunch, arguably)
the 4 approved more recently
As for “Canon 2”, said to be Hippolytan, this is majorly problematic. It’s not the oldest. The facts are these: some few fragments survive of what appears to be an anaphora of the anti-pope Hippolytus (he was later reconciled to Pope Pontian when the Romans - who could care less about internecine Christian squabbles - exiled them both to Sardinia, where they died as martyrs). SCHOLARS DO NOT AGREE on whether the fragments represent an actual anaphora, or a mere commentary on one, or even the work of an antipope who didn’t approve of whatever Pontian was using at the time.
In the 1960s, in a Swiss hotel suite, “experts” from the Bugnini Consilium used those fragments as the “core” of a NEW COMPOSITION: Eucharistic Prayer II.
Those are the historical facts. It’s not, as some would have us believe, that we suddenly restored a third century anaphora. It’s a new composition, with inspiration and some phrases from the surviving fragments.