Brand new sealed Apple service spare EPROM upgrade for version 1 LC PDS slot, AAUI ethernet cards containing the EPROM, replacement part number stocker and instruction sheet. It converts a v1 card into a v2 card by replacing the older 341-0842 ROM with this 341-0470 ROM.
We have been unable to locate any description of what the improvements were but as the two card versions are functionally the same, we suspect it was improved stability/reliability.