Tom,
I don't know when the 39 first appeared (could have been around a long time!), but in the early 70's it was their "entry" Sports Leather Saddle. The lineup included the 39; 42; 80 (several variations); 90 (several variations); There were other models as well (I have some for which I have no reference!!).
I have a 39 and a 90 which I have just looked at for a comparison: The 90 appears to have slightly thicker leather (1-2mm?), shorter side cut, longer nose (completely different profile - more like a Brooks Pro) and the leather is finished off much nicer (beveled). The 90 also has larger rivets and an closed nose adjuster, with stamped identification.
I have my 39 on a Motobecane Grand Touring, and it works fine...looks good on a touring type bicycle, but I wouldn't care as much for it on a racing bike (but this is all subjective!!) because of the side length.
Cheers....hope it stops raining so you can go ride!!!
Chuck Brooks Wonderful Day in Malta, NY
My comments about the leather grade are suppositions only