Pappy,
Are you sure the hilt, collar and butt are nickel silver? Also: The handle is "commando-shaped"...not a "border patrol". Ken is correct, in that ET1 is one line of etching...ET2 obviously 2 lines. The thumb notches are not an option, rather standard on a Model #5. The "Squared" top single hilt is an option and nowadays needs to be specified. It is not a "chargeable: option however and does not count towards the "5". At the time and era that this Camp & trail was made, squared top was the "norm".
As a side note: If you had ordered sawteeth with the usual double hilt, the shop would not have installed thumb notches...and you would have been charged for a double hilt.
Best, Capt. Chris
PS: Did you locate a sheath yet??...CCS