Tom
Numerous minor changes were made to both the TR4 and 4A during production and most of the changes were made mid year, not at the beginning of a new model year as is normally done with cars today.
The exact Commission Number where these changes took place have been debated over the years, and the numbers listed below are from Bill Piggott's "Original Triumph TR4/4A/5/6" book. I listed the what I consider the major changes to the TR4.
There were actually two different colors of white used on the white metal dash TR4. The first TR4s used Spa white for the dash and at CT21267 the color was changed to New White for the remainder of the TR4 run and the Triumph wood dash appeared with the TR4A. Wood overlays were available for the metal dash TR4, but I believe they were an aftermarket item.
Several other changes occurred on the metal dash. The center gauge surround was originally polished metal and changed to a black crackle finish with CT 4399 in early 1962. All gauge glass was also changed from convex to flat glass at CT11308 for left hand drive cars later in 1962.
For 1962 the front suspension was changed at CT 6344 for disc wheels and CT6389 for wire wheels and at some point the front brake rotors and calipers were also changed around this time.
The hood power bulge was changed at CT6429
The radiator changed at CT9553
The engine changed from an open breather system to a closed system (for emissions) at CT15053 in late 1962.
The distributor was changed at CT17954.
Steering rack mounting changed at CT20266 for LHD cars. The seats were also changed around this time.
Carburators changed back and forth from SUs to Stromberg for a short run, returned to SUs for a time before going back to Strombergs at engine CT21471E.
Numerous other changes took place during the TR4 run.
One other issue is the year a Triumph was manufactured may not agree with the year listed on the title. Some states would register the year of the cars as the year it was sold and not the year it was made. so you may find a car the owner says is a 1964, when in fact it is a 1963. The Moss TR4 catalogue lists the Commission Numbers for each calendar year.
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1933 Chevrolet
1962 Triumph TR4
1984 BMW 633 CSi