Patent sets were changed to mark production runs and usually involved detail changes as well. But, there are several patent set changes that have no apparent detail change other than the patent set itself. One of their recurring patterns was to revert back to a previous set.
Most sets appear to have been stamped in one strike, however some individual dates are clearly overstruck/added later with different size numbers and/or dates that don't align with the others. Sometimes overstruck dates came and went while others became part of the regular size and chronological order set.
Another one of their indicators was to drop the last patent for a run and then put it back in a subsequent run. That is why the set with latest patent of 1893 is not at the very beginning of the matrix. The details determine the order of the matrix, not the patents. What they did was drop the 1899 patent for that run. You can see this again in later Dietz lanterns that show a last patent of 1910. Special order or utility marked lanterns made after 1913 usually dropped the 1913 patent. The two 1913 patents, one for the inside flag lift plate and the other for the D-Lite top lift, were mixed and matched several times over the years, while patented details they were actually using after December 1919, like the MAY-4-20 patent for full corner strut lift plate, did not appear on lanterns until 1933. BB