From my experiences, knowing key characteristics for each type of leukemia/lymphoma is what's important (auer rods, DIC, smudge cells, etc). How you classify them.. well frankly, who cares? Qbank tests you over a lot of useless stuff.
And for the record don't learn it as M3, learn it as PML, promyelocytic leukemia. This is the step 1, not the heme/onc certification boards