PP + would + about + past participle

On the structure PP[a] + would + about + past participle I've often wondered if 1) we could use almost instead of about and 2) wether using almost wouldn't significantly reflect on what the sentence means. Do you have any guidelines about it?

For example, I know I should not say or write, "I'd had almost given up hope of understanding it" implying "I'd about had..." I only don't seem to know why. Do you perchance know why? (Of all whys, this one has long bothered me.)

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[a] PP = Personal pronoun