Richard,
I would echo John Thompson's assessment that there is no functional difference between the two versions of Simplex retro-friction levers, as well as the fact that they are generally considered to be the best down tube mounted friction shifters ever manufactured (...although one could also relocate them to the front of their aerobars for "off topic" TT applications).
As for specifics, the first edition Simplex SLJ (...or Super Lucien Juy) retro-friction shifters having the "solid style" alloy levers with the Simplex "starburst logo" were produced from late 1973 through 1977. The much more common to find these days second edition SLJ shifters, often associated with the likes of Sean Kelly and having the distinctive "open hoop" alloy levers, were produced by Simplex starting in 1977 and continuing thereafter right up through the mid 1990's. And while the vast majority of second edition levers proudly display the stylized Simplex logo on their facings, these very same units were also made available as OEM at one time or another for use with several other component manufacturer and/or manufacturer group offerings such as those sold under the brands Spidel, MAVIC, and ultimately OFMEGA (...who absorbed Simplex in 1987). Most of these "alternate" versions bear differing logos apropos their reseller, however, some of these second edition SLJ retro-friction levers can be found having absolutely no logo marking whatsoever.
There is one final note worthy of mention, although to be quite honest I cannot recall all of the specific details off the top of my head and so I am hoping that someone else will chime in here with specifics (...otherwise, I will have to wait until I return home and can drag a few examples out to measure and compare). Basically, I seem to remember that there is a difference in the actual shift levers themselves with respect to the size of the mounting post they were compatible with wherein those produced for use in braze-on applications can accommodate a standard 9 mm post while those intended for use with a proprietary Simplex down tube clamp had a different sized aperture which precluded their fittment in conjunction with a typical 9 mm braze-on post. Whether or not this anomaly was common to both first and second edition SLJ retro-friction levers, or just one or the other, is something that is beyond my immediate recall (...and if no one else answers this question by Friday evening, I will have returned home such that I can research the answer myself).
Robert "Simply Shifty" Broderick ...the "Frozen Flatlands" of South Dakota Sioux Falls, USA
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>From: r cielec <teaat4p@yahoo.com>
>To: Classic Rendezvous <classicrendezvous@bikelist.org>
>Subject: [CR]Simplex Retro-Friction: With and Not With Holes ?
>Date: Wed, 4 Apr 2007 21:05:33 -0700 (PDT)
>
>Ahoy !
>
> I am sort of, kind of, getting prepared to start hunting for a pair of
>Simplex Retro-friction braze-on levers and have recently learned of two
>styles.
> One style lever has a hole in it such that the lever looks like a loop.
> Another style has a solid lever with Simplex logos-type.
>
> What is the difference between the two styles ?
> Only the hole?
> Early or late model?
> Equal performance ?
> Anything ?
>
> Thank you.
>
> Richard Cielec
> Chicago, Illinois; U.S.A.