A simple stihl question, I think!

[oregoncutter]

I have ms440 with the big bore kit I also have two 044s at some point I would like to upgrade. I see there is a 10 and 12mm model of 044s, and a serial number cut off, but baileys doesen't list all 9 digits. Here are the nymbers (144641436) (147096126) (142959570). Also on the label what's the difference between an engine type with a x or a Y.
I know these maybe dumb questions, but can someone please answer them.

 

[Jacob J.]

All of your serial numbers are newer...

 

[oregoncutter]

Hey, thanks! That makes it easy!

Try to stay warm and dry!