The laboratory model badge remained on the C19 & all other laboratory models until the end of production as far as I know.
No records are know to exist for the yearly serial numbers, so there's a lot of guess work involved with attempting to date these by the S/N, but certain design feature changes can help with the later machines.
My C19 came from a one-owner non-collector, complete with record collection which almost filled the cabinet. My machine is serial no.117xxx & I've always thought it would date from around 1921, based on the record collection that accompanied the machine.
There was only 6 or 7 etched label discs, one with the first paper label with the black background (these were only produced for a few months in 1921), and the rest of the record collection were white paper labels made into the electric era.
However, about 60-70% of the white paper labeled discs dated from 1921 to about 1924, and most of these were dance tunes, so I presume the machine was fairly new when the majority of the records were purchased, and that these dance tunes were "the lastest popular hits" when they got them.
The remainder of the discs from about 1925-29 were fairly sporadic & few, so again I presume the
novelty of the machine wore off & the owner stopped buying near as many discs around this time (or they ran into financial troubles). The etched labels were all pretty boring classic type stuff, so I think they were probably poor sellers/old stock when purchased.
None of this is very scientific of course, but personally I doubt my machine was made before 1920 or after 1922.
Then again, you never know how long a machine sat in the factory before being shipped, or how long it may have sat in the dealers store before being sold, and then in my case, how long it took to ship to Australia & get distributed from Edisons warehouse here.
Based on this
guess work, I'm thinking your machine was probably made in around 1925 or so.
If I recall correctly, machine sales started to dramatically decline in 1922/23, so production no's would have declined accordingly.
The most obvious changes made to the later machines that I mentioned earlier included changing the turntable felt from green to a mustard yellow colour, and the governor was changed to hold 3 weights instead of 2. The 3 ball governor may have been introduced in 1926 with the introduction of the long play machines, but I haven't examined one recently to confirm this, but all LP machines I've seen have had green felt.
By the time the Edisonic machines were introduced in late 1927, it appears ALL models across the board had mustard felt & 3 ball governors. Another motor change made at this time was the speed control knob was removed from the top of the bedplate, and was replaced by a knurled wheel in the same place but below the bedplate.
The latest C19 I've found online that retains green felt & a speed control on the bedplate is serial no.152xxx, and the 2 C19's I've found with mustard felt & no visible speed control are S/N 170xxx & 172xxx.
Both these machines also included the 10"/12" buttons to the left of the turntable, but did not include the long play mechanism.
So your machine is obviously from fairly late in the production run being in the 145000's, but I'm guessing not late enough for the felt & speed control changes.
If you get a chance to look, I'd be interested to know if your governor has 2 or 3 weights.
I'd also appreciate the same information from anyone who owns a LP machine
