It is not that prefixes on ionic compounds are “now accepted” but rather that the prefixes may be added when naming any inorganic compound. For example, calcium difluoride and calcium fluoride are both acceptable according to IUPAC. Generally, multiplicative prefixes are always permissible, but may be omitted when there is no possible ambiguity in the stoichiometry. This is likely where the “rule” that ionic compounds don’t get prefixes comes from.
As far as my class, I teach what would be called the “rules” found in introductory chemistry texts, but I also teach my students the purpose of nomenclature: the communication of the identity of chemical formulae without ambiguity as to their identity. I would accept calcium chloride, calcium dichloride, and calcium(II) chloride as names for CaCl2, but also expect students to produce the correct formula given only “calcium chloride.”
You will also see oxidation numbers used in molecular compounds, if the situation calls for it. For example, NO2 is nitrogen dioxide to most of us, but also may be named as nitrogen(IV) oxide.
I highly suggest reading Adrian Dingle’s excellent blog post on this matter. I came across it last year and was glad to see that he had put a name to the “non-ambiguity principle” I had previously used without a name and cited IUPAC support for it.
https://www.adriandingleschemistrypages.com/nomenclature/why-you-should-stop-worrying-so-much-about-nomenclature/
As a side note, Adrian and I have been unable to identify the origin of the “rules” so many textbooks claim are written in stone. If anyone has any insight, please share.