I did some additional looking. I found a thread about these from a few years back. It's here:
http://www.bladeforums.com/forums/showthread.php/1043923-Barlows-for-Dog-Lovers-Ka-Bar-Lo!!!. I'm going to quote forum member Hawaiianhawk below. Mine is in good shape but has some hallmarks of age. It seems like it's about 30 odd years old. Here goes:
"From the Kabar forum, courtesy of Paul Tsujimoto, senior engineer for Kabar:
The KA-BAR -LO was a tradional Barlow produced by KA-BAR. I don't have the exact dates but it was produced in the 1920s. KA-BAR produced the Barlow up to the 1970s.
The 1920s KA-BAR-LO came with black composite and smooth bone handles.During the later years that changed to Delrin. "KA-BAR-LO" was stamped transversely across the long front bolster.Of course the stamp changed from 'KA-BAR' to 'ka-bar'during the 1960s. There were two versions: a Spear point main blade and pen; and a Clip point main blade /pen combo. The Clip Bladeknife was designated with a 1/2.
In 1983 the KA-BAR Collectors Club Knife produced a Dog's Head Version in Stag with "KA-BAR-LO" stamped longitudinally on the Bolster. In 1985 a Dogs Head Version in Jigged Bone was produced; No stamping on the Bolster. In 1990 a bent Barlow was produced with a Clip MainBlade and Jigged Bone in Green and Blue.One had a dogs head, the other had an oval shield. No Stamping on the Bolster."
Thanks, obviously, to Hawk and Paul for the info. Hope quoting the post was okay.