Help With Ike Varieties

I am getting serious about Eisenhower dollars and am confused about the varieties. Between the coin facts section of this site and the Red Book, I have derived the list below -- this is what I think a complete set would comprise, not including any varieties. Did I miss anything?

bus = business strikes, prf = proof, x = ones I have already

1971 bus clad x
1971-D bus clad x
1971-S bus silver x
1971-S prf silver
1972 bus clad x
1972-D bus clad x
1972-S bus silver x
1972-S prf silver
1973 bus clad
1973-D bus clad
1973-S prf clad x
1973-S bus silver
1973-S prf silver
1974 bus clad x
1974-D bus clad x
1974-S prf clad x
1974-S bus silver
1974-S prf silver
1976 bus clad x
1976-D bus clad x
1976-S prf clad x
1976-S bus silver
1976-S prf silver
1977 bus clad
1977-D bus clad x
1977-S prf clad
1978 bus clad x
1978-D bus clad x
1978-S prf clad x

As far as I can tell, only 1971 and 1972 Ikes from Philadelphia have varieties, is that right? Or do the other mints have them for those years too?

And there are two varieties for each of those years, which are identifiable by the islands off Florida on the reverse. But the Red Book shows a third one, although I don't quite get that one. How could I tell?

I also surmise that 1976 Bicentennial Ikes from all three mints have two varieties each, and that it is a matter of bold or light lettering on the reverse.

The $64 question is, do I need the varieties to have a complete set? I especially think (from the pictures) that the 1976 ones are not different enough to matter, at least not to me.

I'll appreciate any comments on this. Thanks for listening.

Jan