To clarify and answer the question:
All
Presidential dollars are supposed to have edge lettering. Some don't, thus are errors. Since they were sporadically created, any original roll could contain any quantity of the plain edge coins, so no - it would not be the whole roll.
Caution on two things:
1. If you're ordering or buying numbers of rolls looking for these, you are probably wasting your time. They are extremely difficult to find.
2. If you are purchasing them as single coins because you want to collect them, learn how to tell the difference between the real errors and coins that have the edge lettering sanded off. There are more fake errors out there than the real ones. Best bet would be to buy them in slabs.