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I'm not sure what is meant by verb one and verb three. Also, I don't see why that form can't be used in the past perfect tense (but I'm willing to be convinced).
I agree with Lib- 'have to' and 'be able to' are not exactly modals, but are used as ways of filling in for 'must' and 'can' respectively in forms that cannot be expressed by the modal, like futures with 'will', perfect aspects, etc. ;-)