How many boiling points does a mixture of liquids have?
I do use my comment above because the meaning of the books is, with little interpretation, clear and the answer is simple and don't require digging in theory of fractional distillation. So it would be pity to let the question unanswered.
A mixture as those discussed boils over a range of T in the sense that its boiling point BP depend on its composition.
The actual mixture, i. e. at a given molar ratio, has one well defined BP (at given P).
If you do not look at a given composition, but you actually conduct a distillation, as the boiling change composition the BP changes all along the process/column/plates, actually spanning a range of T.