Looks nicely kept, a good example. Did it took you long to find it ? Or was just a casual finding ?
I also got in touch with RJ and got a similar answer. I am starting to believe in the same you have found, that Plaubels older than the Makina II had no body serial number. Hopefully RJ will be able to thoroughly check his cameras and locate it if in another position, or not find it at all which could hint this no-serial theory.
It's odd that some people rejects to share their serials on the grounds that they can be misused e.g. on eBay. Such has been the case of Mr. Jani Heikkinen, which declined to provide data about his Makina III even after linking this thread which would allow "misusing" with or without his single number... Pity, but perfectly respectable! Luckily there are other, friendlier owners and sellers which are participating.
To try to have increased visibility, and a more ordered way to present the data, I have created a little "table" at the discussion page on the Makina article from camera-wiki:
A local friend has shared the serial of his chromed IIS with me: 1H476. It is actually the first one we find starting on "1", so it may seem that for other serials, the first character is a zero and not a capital 'o'. But, based on the data collected so far, looks intriguingly different...
As for the export models, I can't say for sure. In my experience with folders, I don't think so. Distances in feet are common in the UK for example, so there are Agfa's with distances in feet and the same cameras branded as Ansco - Agfa's importer on the US - also in feet. It could be that batches were made taking into account its destination. Who knows ! Maybe the actual Plaubel, if they keep something from the last century...