I'd say that's entirely your own speculation, I interpret the two as meaning exactly the same except powered-lift has been added. I've even read the preamble for this change which says nothing about extending the scope to cover an instrument rating, it only mentions powered-lift.
The preamble only mentions powered lift. But the regulatory language changed in other respects, from
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(f) Instruction in multiengine airplane or helicopter. He may not give flight instruction required for the issuance of
a certificate or a category, or class rating, in a multiengine airplane or a helicopter, unless he has at least 5 hours of experience as pilot in command in the make and model of that airplane or helicopter, as the case may be.
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to
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Training received in a multiengine airplane, a helicopter, or a powered-lift. A flight instructor may not give training required for the issuance of a
certificate or rating in a multiengine airplane, a helicopter, or a powered-lift unless that flight instructor has at least 5 flight hours of pilot-in-command time in the specific make and model of multiengine airplane, helicopter, or powered-lift, as appropriate.
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As the Chief Counsel indicated in a fairly recent opinion letter, the preamble is the preamble, but the rule as written is what counts. And that was in a case (currency approaches in a sim not requiring an instructor) where the preamble was quite explicit about what it intended, not merely silent.
The removal of the "category or class" language pretty clearly indicates the rule, as of 1997, is not limited to "category or class" ratings.