DR2 question ?

I am looking a 256mb module to add to my Acer laptop. The existing module
has on the label ;

PC2-4200s-444-10-C1

What is the significance of the last 2 settings. Looking at photos of
modules for sale on Ebay a lot of items have similar markings but ending
with the likes of 12-C1 or 11-C0. Would these work ?

TIA