No. L 129
This pen is from the personal collection of specialk0449 - a generous contributor on FPN, and now this website!
L to R: 138, 129, and 139
The 12x was produced for only a short time from around 1935-40. The L129, in particular, seems to have been produced after two or three years of success from the smaller sizes. Collectible Stars I scores the L 129 a 9 out of 12 points in rarity. From my experience, it is far more difficult to find (and afford!) a 129 in comparison to the 139. As seen in this advertisement from the late 1930s, the 129 was priced at RM 50. Compare this to the RM 45 price of the 139 in catalogues around the same time.
Rösler, J., & Wallrafen, S. (2014). Collectible Stars I: 1908 - 1947.
The first time I held a 129 in my hands I was surprised by its size. I was expecting it to be as large as the 139, but it was very apparently smaller. I don't like big pens and so the 129 was a perfect fit for me, but I was confused by the fact that it was so much smaller. In the pic here, you can see what I mean. The 129 measures 12.8cm capped, the exact same as the 136. Also, the 129 measures the same size as the 128 - the clear difference between them is that the silver rings are only found on the 129. Also, it is interesting to note that the 129 and 128 have the same nib size - a '245' or size 8 that is found on the 138. The 139 nib is larger.
The nib on the 129 is made of 14c gold. While the 13x series pens were found with a variety of nibs like gold, steel, and palladium, the 12x series pens were found mostly in gold because this model was produced before WWII (during which pen companies were forced to look for substitutes to gold).
Finally, the 'L' in the L129 stands for Luxus or luxury. Considering its price and distinct silver rings, I am assuming this pen was maerketed as a luxury writing instrument.