[noun] + 乃至 + [noun]
[noun]、[noun],乃至 + [noun]
[number] + 乃至 + [number]
乃至 adds a last item that goes further than the ones before it: "and even", "up to". It joins nouns or noun-like phrases, and the item after it is the wider or more extreme one. It is written Chinese – reports, essays, news.
The items climb a scale: a city, then a province, then the country; a year, then a decade.
Between two numbers, 乃至 marks how high the figure can reach.
甚至 is an adverb as well as a linking word, so it can go straight before a verb: 他甚至忘了 "he even forgot". 乃至 only joins items in a series and can't stand before a verb that way.
The item after 乃至 has to be bigger in scope. Reversed, the sentence makes no sense.