A theory that I have had for a short while now is that the Empire/ Empire State model is a continuation of the LP B model, that the introduction of a new model (M designation finally) created the model names "Artist" and "Empire".
It is worth noting that the appearance of the first two model names seems to be simultaneous with the disappearance of the "LP" designation and is closer to 1930 than 1920.
The "Artist" was the "new" model (still theory..) perhaps with a modified bore? The simple numerical serial sequence covered both Empire and Artist models until the numbers reached about 20,000, then the letter designation was introduced due to the higher production numbers during the 30s and from there on, the models have separate numerical sequences with "H" designating the Empire, "M" designating the Artist (theory without more hard evidence). Then a new model was introduced that was somewhere between the two and that was the "L" model, which became the new Artist. The "M" model continued but was renamed the Brilliante? This last statement is almost certainly what happened because as soon as we see the Brilliante model, it carries the M designation, and Artist models have either no letter (earliest) an "M" prefix (middle period for the model), or an "L" prefix (later models after "M" was renamed Brilliante).
I haven't inspected enough of these to know just what the differences are that constitute a particular model. I am beginning to think it is probably in the bore specifications. Early on I thought that only certain models could get the silver plated keys, but then I found an Empire with silver plated keys. For a while it appeared that LP B and Empire models both had bakelite bells; but the Empire with silver-plated keys also has a wooden bell. None of these appear to have substituted parts and all have matching trademark styles on all of the parts. There are also two very distinctive key-work styles and those don't appear to be tied to any particular model, but perhaps might be tied to a particular period of manufacture? And then there are the ones that are clearly marked as imports from either Germany or France and these are not the early ones, but appear to be post WW2 and some of those have two serials on both joints.
It is far easier to follow the history of a maker like C.G. Conn or H. Selmer, Paris. Conn had only two serial sequences for the entire history and Selmer's sequence is very logical. Breaking Penzel Mueller's system requires raising Alan Turing from the dead almost.
The timeline will become more complete even if only a few people add entries now and then. I have noticed that since I have been sending questions about the serials to sellers that don't provide it up front, many are now including that information in the auction listings and a few have even commented that they visited this site looking for date of manufacture information. That has helped me fill in the blanks, but what really helps is when an original owner reports a story or when someone has a dated advertisement or part of the paper work. Believe it or not, some of the most helpful information has come from reed envelopes that have music store stamps on them. In those early decades, Americans were not so transient. Most students bought an instrument from a local music store and continued to buy reeds from the same local store. If it's a pro instrument, then it might have toured, but many pro players toured only regionally and still bought reeds at home. Googling the names and addresses of those stores sometimes turns up historical advertising references in archived newspapers. One can find out what era the store was in business. Some of them were in business for decades, some are still in business. When one finds a sole proprietor then it's often just a few decades.
And then there are quite a few instruments that have military band designations of one sort or another. Small companies like PM continued to make musical instruments during the wars while large factories like Conn were converted to war machinery production temporarily. H.N. White and Conn made less of those instruments because their factories were diverted to war efforts while Bettoney, Penzel Mueller continued to make band instruments for the military bands. We can infer that when we see a large grouping of serials that are also "US" stamped in large letters that these are war production periods. These groups of military instruments, mostly Brilliante "M" models, also have serials that support the theory that models had separate numerical sequences. The production numbers were simply too high for there to be only one numerical sequence after the introduction of the letter prefixes.
