ETA: I'm not even playing with a regulation deck!

At least 2 of the knives I posted below are not even jackknives, as Jeff specified.
EC Simmons Keen Kutter (pre-1940, right?):
Landers, Frary, & Clark (I read that they discontinued their cutlery division in 1950, so this knife should meet Jeff's time requirement):
Imperial MOTS (1936-1952 tang stamp):
OK, now I have to draw TWO knives to fill the "inside" of a straight (not a play I'd usually make).
Kingston cattle knife (I have a 1947 catalog clip that shows this model K-320, but I've read that Kingston Cutlery was formed in 1943 but started fading in the late-1950s.
This thread by
@Codger_64 does NOT list K-320 as appearing in Schrade/Ulster/Kingston records for 1959. But was my knife made prior to 1955?? I don't think I have any way to know.)
Case XX two-blade congress (Similarly, the tang stamp for this knife was used 1940-1964, so my knife may be pre-1955 or it may be newer than that. Who knows??)
So, Jeff, I'd probably have to say I'm busted going for an inside straight!

- GT