While we wait for Bill, here is the current JASO ratings listing system, fresh of a few months ago.
http://www.oilspecifications.org/articles/JASO_MA_JASO_MB.phpNote please that they have changed their nomenclature again, they have a JASO MA, JASO MA1, JASO MA2 and JASO MB in their nomenclature, with each classification carrying a separate meaning.
(Bill's 4T is a Mobil 1 advertising gimmick that carries no real meaning)
Note please, that none of the JASO MA group of standards have anything to do with ZDDP content -- they merely describe what the oil in question does when subjected to the JASO T 904:2006 clutch system friction test.
Remember always that the Savage engine has unique requirements that no longer fit the JASO categorizations very well. We can no longer trust a JASO rating to tell us if an oil is good for the Savage or not, especially since they keep changing and multiplying their various standards.
That is why we bother to keep a recommended oil listing in the Tech Section.
Plus, JASO has plumb gotten a little weird ..... and we know some games will be played by some oil makers using this particular statement.
If all three properties of a JASO MA oil fall within the limits specified as MA1 then the oil can be classified as a JASO MA1 oil. If all its properties fall within the limits of MA2 then it can be classified as a JASO MA2 oil. If some properties fall within the MA1 subcategory but others in MA2 then the product is simply a JASO MA product.