The one that is 11" long and has a cool rib pattern carved into it has what appears to be a NO1 Lee-Enfield rear sling swivel (or similar) installed in the plug, which suggests to me it is not very old.
A lot of very old horns have seen bad repairs, and replacement of parts from newer sources, including gun parts. The age of the horn may be much older than the parts. All a newer part indicates is that someone put it on the horn after that part became available. You can not generalize about the age of the horn from one added part.