It's not 100% more — 100% would be twice as much. In this case, we've gone from none at all to having some, which is infinitely more.
(a, b, c, d) = range(4)
(a, b, c, d, e, f, g, h) = range(8)
It was twice as cold on Monday than it was on Sunday. /duck
Can quickly go from 300 K to 150 K, source https://ars.els-cdn.com/content/image/1-s2.0-S00191035163048...
It went from having 0 pattern matching to having 1 pattern matching -- that seems like '100% more of this thing we are talking about' to me. This of course only makes sense if you see '1 pattern matching' as a precisely defined abstract construct, but I guess the 100%-more joke usually requires that perspective (and is a joke precisely because it's so non-sensical to think this way).
This is what people normally learn in primary school about the meaning of this phrase.
That also matches 'biannual' (an event that occurs every other year is 'biennial'), so 'biweekly' as 'fortnightly' is certainly to be proscribed, in my book.
Except that's literally the dictionary definition of the word. And "biennial" and "biannual" are synonyms.
I only have Collins' concise to hand, which gives the definitions I have and doesn't even mention (not even proscribed or US etc.) other uses. And Collins is pretty permissive.
And no they're not. 'Biennial' events occur once per two year period; 'biannual' events occur four times per two year (twice per year) period.
For example, in horticulture 'a biennial [plant]' is one that has a single flowering/reproduction cycle over two years. (Cf. 'annuals', 'perennials'.)