Google Books and the Kraeuter catalogs themselves (you can find them on Internet Archive International Tools Catalog Library) are just as confusing about "Gripkut"!
Without drawing any conclusion, I will tell you what I have found...
/ The "Gripkut" name (note, no "-Junior-") shows up, along with other early Kraeuter names "Victor" and "Dreadnought", as early as 1917, as evidenced by
this Chilton Automobile Directory.
/ The "Gripkut" (note, no "-Junior-") shows up on page 6 of a Kraeuter catalog dated 1921, where it's called "the latest Kraeuter creation" and a "Design patent plier." Linked
here.
"Latest creation" (in 1921 cat) seems to jibe somewhat with the earliest reference (1917) I can find on GB. "Design patent plier" sounds past tense to me, not pending, which might suggest yours was made sometime between 1918 and 1921. But that's when things go haywire.
/ There is a whole page dedicated to "Gripkut" pliers in the 1934 Kraeuter catalog, which also states they are "(Patents Pending)". Linked
here.
How can they be "Patents Pending" in 1934 if they were a "Design patent plier" in 1921? Different patents?
I have not looked further than that yet.