Can anyone tell me what this is? Guessing it is NOS and now phased out / replaced. May be narrow kerf as it looks a little less wide than my Carlton K3L
There is no way it is narrow kerf if it is .063. However, the width of cutters vary on regular chain as well, and semi-chisel will be slightly narrower than chisel up front.
#25 likely just is the recommended raker setting - that is .025 on most .325 chain.
#19a on Oregon .325 drivers sounds like something old, as it doesn't fit the system used the last few decades.