I promised then to look at what happens after negation. Here are the options (sticking with contracted have):
Again, I'm looking for these in the GloWBE corpus of English from the web. When I search for the of variants, I have to specifically search for a verb after the of in order to block out things like of course or of necessity, where the of isn't standing for have.
could not 've could not of couldn't 've couldn't of
The full not versions in the first row of the table offer no surprises. Just as with the modals, there are more of spellings in the British than in the American (126 v 86).
First, the expected news: the of variants are more common in BrE, just as they were in the non-negated data. 85 American occurrences v 170 BrE. Here's the top of the results table:
As you can see, some verbs show greater numbers with AmE, but this is to be expected because the numbers are small and because some of the verbs are used more in AmE than BrE--like figured, which is cut off the table. What's most important is the fact that the British total is twice as high as the American.
Is that just because BrE uses the present perfect (the reason for the have/'ve/of in these verb strings) more than AmE does? If that were so, we'd expect for the 've form to be more typical of British too, but that's not the case:
The tables in the previous post make this case more strongly, since here have the complication of whether people avoid writing double contractions. To test this a bit further, I've looked for another double contraction: 'd've, as in If I knew you were coming, I'd've baked a cake.
Looking again at whether of is used instead of 've, it's still more British (59 total) than American (26 total) after 'd. Here's the top of the list:
So, it's not looking like British writers avoid double contractions all that much more than American writers--unless writing of instead of 've is part of an avoidance strategy.
I found it interesting in the sheet music pictured above (and more than one version of it), it has been printed with a space before the 've. That's another solution--and perhaps that was more common in earlier days? The corpus would not distinguish between the space-ful version and space-less.
And on that note: