I recently acquired a very nice condition Voit Lung with the blue label from Rob at thescubamuseum.com For those of you not familiar with this particular model, it is unusual in a number of ways. First, both of the cans have a satin finish. Secondly, the internal mechanism is that of the USD Mistral design. It is not the Voit version of the upstream valve, as seen in the Polaris 50 and last generation Blue 50 Fathom V-55 models. It also has the same label as that of the Voit VR1, with the difference being the blue paint rather than the green.
I had the opportunity to service Rob's example a few years ago, and was surprised to see that the Mistral venturi was not perpendicular to the valve body. It was slightly canted. Initially, I thought this was just coincidental, until I discovered that another two examples owned by VDH members also had the venturi tube canted in the same fashion. The top can (valve side) only has one indexing hole for the locating pin. When examined, you can see that the offset position of the venturi tube aligns it down the approximate center of the inhalation horn.
If you have one of these unusual blue label Voit Lung regulators, please add your serial number to this thread. I am making an attempt to determine approximately how many were manufactured by the range of known samples.