Hello,
I don't have a great knowledge of the Ontario M10 and Lan-Cay M11, so you'll better wait some more answers.
Anyway, I believe the main difference between the "standard" M9 bayonet and the Ontario M10 is (apart from the blade markings and the handle you mentioned) the scabbard configuration. The "loops" at the end were removed and the back weebing was modified.
The Lan-Cay M11 is just not a bayonet at all, but an EOD tool (knife, in fact).
I personally wouldn't consider the Lan-Cay EOD an improvement, as it was just a different configuration of the M9 bayonet.