There is no relay failure, just an incorrect implementation of Mirrored Bits.
First, talking about SEL-2506. That is a simple device with no additional features like fallback values of MB, it merely follows data received (with an option of security counts).
If a data packet is lost it...
Are you sure it will help you?
Purely hypotetically I can send you some ProTest test plans for the relays you mentioned but they are for the relays that I've got; and they are different from yours. You will have to re-design those test plans anyway as you relays have different settings and...