Interesting stuff, for sure.
Stihl used to have 4 different sizes of any particular cylinder and piston. They were lettered A, B, C and D. When replacing a piston for a C cylinder, you had to make sure you ordered a C piston, etc. The reason was that the chroming process at the time wasn't exact, so they would measure each cylinder after the process and label it with a letter, then match it with a similar sized piston. Since the chroming process has improved, they only provide one size of replacement piston these days and no longer letter the cylinders.
Where did you get the idea that all saw chain was chromed? There is unchromed chain still in use today for fitment on the very cheapest saws made, usually electric saws. And of course there is carbide chain, Lemery chain as well as diamond chain, all of which are not chromed.
I know the piston skirt retains oil, that's why they have horizontal etchings on them. And since the chrome on the cyl wall is somewhat porous, it would prolly retain some as well.
Did you know that Stihl had a brief experiment with chromed pistons? It didn't last long, and I don't think I ever saw one.
A few years ago at one of the service schools they had made a really interesting teaching tool. They had drilled a hole in the top of a cylinder on a working chain saw and inserted an extremely high speed camera. Then they were able to start the saw and show the combustion bloom in extreme slow motion, and how different fuels effected it. I guess you had to be there, but it was fascinating to everyone who saw it.