First if you are a BCCI member there is a 319 Rancher history on website.
Second :
Photo of the two 319s, L shaped awl in back, L is visible from reverse (Trax)
Three of the four 307 Wranglers, missing is yellow scale. Back one is marked: BUCK,MadeInUSA, 307 on reverse of tang.
Here is wild as guess, mostly said by Flat already:
In 1989 the last of the brass liner knives were made for Buck by Camillus, with the 1990 model design change Buck went in house making them in all Stainless, lintergal bolsters and liner and SS springs. This design change eventually ousted the brass liner knives as the parts ran out. The 'fab' four were manufactored by Buck in plant. I guess they didn't want the expense of all that extra tooling for lower volume sellers....plus what Flat said about the 700 series. Some 'other' models were occasionally made by Buck such as the 312 and 314 Trappers but Camillus made a few models also, contracted by Buck thru them for other people, i.e. SMKWs 329,322, 331, etc. What was interesting was all the new Bucks that were on _bay as Cami.factory was closing. You think they were real, but then you see the brass spring rivet where a SS rivet should have been...haha odd. The 307 was a big stockman, good for country boys and cattlemen, not so desired by sub-urban caboys.
Flatlander was right on...
300Bucks
PS. The 319 spiral awl was carbon steel and will rust.......