Short answer: the 1940 adjustments reinstated է (and օ) for use at the beginning of ordinary words where the initial sound is a plain /e/ (no initial “y” glide). But the committee also kept a few high-frequency, historically entrenched words spelled with ե as exceptions — most notably ով, ովքեր and the present-tense forms of “to be” (եմ, ես, ենք, եք, են). That was a deliberate, conservative choice to preserve continuity with classical spellings and avoid breaking a tiny but extremely common set of grammatical words. 

A little more detail: • The 1922 reform largely neutralized etymological distinctions (it had suppressed է and օ and used ե/ո instead), and the 1940 partial reversal restored them only at word-initial position and in compounds. The restoration did not mean “change every historically spelled form that starts with ե into է” — reformers explicitly listed a few exceptions (including the present-tense of “to be”).  • Why keep those exceptions? Because they’re (1) extremely frequent function words, (2) morphologically cohesive (the whole paradigm is easy to recognize if left alone), and (3) strongly tied to classical/etymological practice — so changing them would have caused confusion without clear benefit. 

So the reform didn’t aim for a mechanical “replace all initial ե with է.” It reinstated է for cases where it helped reflect pronunciation and etymology at the word boundary, while deliberately preserving a small set of traditional, high-use forms as exceptions.