One difference that surprised me was the listed scale length - the Electromatic Junior Jet is 30.3" and the Streamliner Jet Club is 30" per the Gretsch site. The neck inlays are interesting - they call them thumbnail inlays on the side of the fingerboard. Gretsch is also at least using different names/language for the pickups - 'Low Down single coil' on the Jet Club and just "Gretsch single coil' for the Junior Jet. It may be the 30.3" vs 30" scales and pickup naming are just differences in the labels/names/descriptions and it's essentially the same neck geometry and same pickups, but then again maybe not.