The images below are two scatterplots of Model 19 serial numbers by the label they were found under (Camro 28, Minca 28, Delco 828), created for a presentation on the subject. Though more serial numbers have been recorded since these plots were generated, the new numbers fit into the patterns well enough that the plots still give a valid representation of distribution.
The intent is to show how the serial numbers found among the three models might suggest the order in which those models were put on the market. Though the evidence is not overwhelming, it does suggest that Camros were first on the scene, followed by Mincas, and then Delcos.
For reference, the range of known serial numbers across all known Model 19s is from just over 100000 to about 154000. The serial numbers are almost always found in these cameras with a '19-' prefix, but the six-digit portion is assumed to be the 'significant digits'.
In both cases, the Camro 28s show up most prominently in serial number ranges from 100000 - 113000; Minca 28s show up from about 113000 - 138000; and Delco 828s show up most densely above 138000. That said -- there are visible scattered instances of Mincas above 138000, and Delcos have the greatest 'overlap' into the 'densest' range of the other models. This is not particularly surprising, since almost all Minca 28s and Delco 828s have a lens labeling faceplate that screws on over the front of the lens barrel, and alsost invariably, a Camro 28 logo is found under the Minca or Delco faceplate. All known Camro 28 logos are painted directly on the front of the lens barrel.
