DIMAP/NODE and ODE contain exactly the same two senses. Of these, sense 2 is quite narrowly defined and at a stretch could be seen as related to, if not an extension of, sense 1. As is remarkably straightforward in prepositional use; while a few phrasal prepositions can substitute for it, no other simple one can (though “like” is close in some cases), and the presence of as is a clear sign that a classifying or characterizing statement is being made.
Notes from the spreadsheet:
No additions were made to the inventory.
Other instances of as that may deserve idiomatic treatment:
There are several phrases in ODE, some of which you have isolated as separate prepositions in DIMAP (as for, as from, as of, as regards, as to). As per is probably worth adding to this list. As it were is easily isolatable and does not function as a PP. The pattern as + adj/adv + as is adverbial and used in comparisons; presumably this is what is discussed at Quirk 7.86 (haven’t got the book with me now). Most of the hypersense instances of as are this, not a prepositional sense.
Other Notes:
ODE’s sense 2, “during the time of being (the thing specified)” seems almost to have been devised for the illustrative sentence: he had often been ill as a child. Given the broad wording of sense 1, it would not be too far a stretch to simply subsume this sense under it. Random House Unabridged gives only one sense of as preposition: “in the role, function, or status of.” I have left ODE’s sense intact, even though there are no instances of it in FrameNet. It does perhaps stand distinct from the overwhelming variety of cases where as is used in that this sense (2, that is) is relatively free syntactically because it typically modifies a whole clause: Thus he had often been ill as a child. = as a child he had often been ill. = often, as a child, he had been ill.= he had, as a child, often been ill.