Lovely Floris Meydam for Leerdam ashtray, appr. 15 cm wide. I was looking out for one of these striped pieces, so I am quite happy to have found this one

One question: according to
>> Botterweg this is a "Serica" piece (no. 5).
Here is another one, signed as well:
>> LinkMost of Meydam's striped pieces seem to be signed (= Unica pieces).
So is the difference in the numbers produced from each pattern? Or was it just more or less arbitrary which one was marked Unica, and which not?
Thanks,
Michael