Aught to know better

 A few years ago I wrote (here) about "for aught I know". And I'd been chewing away at this piece of gristle for some years before that: a note in my 2014 book When Vowels Get Together V5.2 I wrote  this, in a note about words that use the spelling -augh-:

<prescript> 

(... the less common words aught and fraught [are] not included in the main /ɔ:/ section, as even the most advanced student is unlikely to need these. They might very occasionally meet them, but chiefly in the idioms 'for aught I know' and 'fraught with difficulty/problems/ danger...'. Even then, in the first of these the archaic 'aught' – meaning 'anything'...

 <2026-correction>
(or 'nothing'[(cp Mr Micawber's 'twenty pounds, ought and sixpence']; I was led astray by the initial a)
 </2026-correction>

... – is often replaced by 'all'; the British National Corpus lists 55 instances of  'for all I know', but only 2 for the earlier form.)

<correction date-"2026">
In fact the words 'not included in the main /ɔ:/ section' are wrong there. But although I've known about the mistake for some time I haven't been able to correct it – for various reasons having to do with operating systems and reverse compatibility; don't ask. TBH, as we hip-cats say, I don't remember the details.
</correction>

</prescript> 

My latest foray into this bit of linguistic archaeology is to compare the fortunes of the two phrases "for aught I know" and "for all I know" using the Google Books Ngrams Viewer:

A tale of two fortunes

In the mid-nineteenth century the version with 'aught' was 5 or 6 times more common than the version with 'all'. Sortly after the turn of that century the two were equally common. Almost immediately "for all I know" established a healthy lead, staying at 3 or 4 times as common as its rival, until the turn of the twentieth century, when it suddenly shot up, increasing its lead to 7 or 8 times. In another few years, the 'aught' version will exist only in the speech of a dwindling few old fogeys and in historical texts.

What's the reason for this change? Part of the answer, as it applies to the USA, is here (quoting from my 2022 post):

<prescript>

The Department of  Security's Yearbook of Immigration Statistic 2012  shows this pattern of immigration since 1820 [HD: 2026 when that Google Books Ngrams Viewer graph picks up the story]...: 

It's not difficult to imagine what was going on in the mind of the ESOL speaker: they hear a first-language  English speaker saying 'for aught I know'. The second syllable is a word they don't know (or think they may have misheard) starting with the vowel /ɔ:/, so when they reproduce the phrase they use the 'all' version. 

</prescript>

But what caused the steep rise in the 'all' usage noted in the Ngrams chart  in the first quarter of this century? I have no (mature) idea, although I suspect computers are involved in some way. 'FFS' as they used to say in the OSI standards world when something needed further study.

And another thing: the story with 'for aught I care' and 'for all I care' is very different (but with a similar recent steep rise for the 'all' version): 

Curiouser and curiouser.

Time to return to the madding crowd.

b