The phrase now attached to a list of seventy-two angels began as something considerably narrower.
Shem ha-Mephorash is usually rendered the explicit, distinguished, or separated Name. In its earliest usage it refers to the Tetragrammaton, the four-letter name of God, and specifically to the pronunciation of it that was reserved. The Mishnah, at Yoma vi.2, describes the high priest on the Day of Atonement pronouncing the Name, and the people prostrating themselves on hearing it. That is the setting: a name spoken aloud once a year, in one place, by one man, and otherwise substituted for in reading.
After the destruction of the Temple the pronunciation lapsed, and the tradition of substitution hardened. The Talmudic passages about names of twelve and forty-two letters belong to the same world, restricted knowledge, transmitted under conditions, about how the divine name might be extended or expressed.
The later application of the phrase to the seventy-two-fold derivation is therefore an extension. It takes a term for the ineffable name of God and applies it to a set of seventy-two syllables extracted from a narrative passage by a counting procedure. Whether that extension is a natural development of the idea or a substantial change of subject is a question on which the tradition itself is not univocal.
There is a further shift when the seventy-two are given suffixes and treated as angels. At that point the names are no longer parts of the divine name at all; they are the names of created beings, each with a domain. What began as a way of speaking about God has become a directory of intermediaries.
Both usages are current, often in the same book, and readers should be aware that the phrase does not mean one thing.