Robb Stewart has put together some improved serial number dates based on more recent discoveries. His data can be found here.

Below are my original guesses as to beginning-of-year serial numbers for pre-1952 Olds horns. You can read my reasoning for the pre-1946 numbers, or the 1946-1952 numbers . In arriving at these numbers I have attempted to reconcile the Robb Stewart data with the firsthand reports. I welcome any evidence that can help me improve on these guesses:

Note: According to longtime Olds employee Don Agard, the trumpet and trombone serial number lists were not combined until 1953. This conflicts with the Robb Stewart article, which was also based on interviews with former employees. Since this began as a study of trumpet serial numbers, most of the data collected has been from trumpet owners, so the impact of this discrepancy is probably minimal on the actual trumpet serial number charts. However if Mr. Agard's account is correct, trombone serial numbers lagged behind trumpets until they were merged in 1953. According to Agard, the last 1953 trumpets being in the 68,000 range while trombones in the 48,000 range. This does not agree with the published serial number records, which indicate that they reached 90,000 in February 1953 and 100,000 in October 1953. I don't know how to reconcile these accounts so I'll just present them as data collected. At worst, they create some uncertainty for manufacture date of trumpets/cornets in the 70,000-100,000 range (but the uncertainty is at most a year or two). For trombones, the uncertainty for horns prior to 100,000 would be substantially greater. Note that discovery of a trombone with a serial number between 48,000 and 100,000 would disprove the Agard account. I don't have evidence that such a trombone exists but I haven't really looked hard for it since my focus has been on trumpets and cornets.

UPDATE: I now have a report of an Olds Recording trombone s/n 56,668. That suggests that trombone serial numbers went higher than previously thought before the merger of trombones and trumpet into a single serial number sequence.

Jan 2004: an Olds Super trombone was seen on ebay with a serial number of 54,571...even including a nice closeup of the serial number. This doesn't completely disprove the Agard account but at least it means trombones went at least to 54,571 before the merger Agard describes. We would need to see trombones in the 6x,xxx / 7x,xxx / 8x,xxx / 9x,xxx ranges in order to dispute Agard's account with much confidence.

Aug 2006: Revising the early trombone dates due to discovery of #4016 with original paperwork showing a manufacture date of 1923!

trombones 1915 260 1920 1260 1923 4000 1925 6000 1927 7000 1930 7300 1931 7700 1932 8000

trumpets 1929 101 1930 1700 1931 3300 1932 5000

All Brasses
1933	8250	s/n lists merged in late 1932 at around 7000
1934	8500
1935	8750
1936	9500
1937	10250
1938	11000
1939	11750
1940	12500
1941	13250	production curtailed after US entered WWII 12/7/1941
1942	14000	S/n 14005 made in May 1942, from original warranty card
1943
1944
1945
1946	15000
1947	21000
1948	28000	Ambassador introduced at around 27,000
1949	36000
1950	45000
1951	56000
1952	70000

Miscellaneous milestones
1948	Late 1948, serial number 35xxx Olds Studio, earliest example I've seen
1948	around 28000 (perhaps a bit earlier, for the fall 1947 school year)	introduced Ambassador trumpets and cornets
1950	between 45,8xx and 49,6xx	replaced Super Recording with Recording model
1952	somewhere around 70,000	introduced Mendez model
fall 1955	between 149,6xx and 150,3xx	moved production from LA to Fullerton
September 1956	s/n 189,611	elimination of the large-shank mouthpiece receiver on cornets
Spring 1958	between 246,5xx and 248,8xx	redesigned Ambassador cornets & trumpets. Pinky ring changed to pinky hook. Also bracing changed.
1964	around 450,000	Alliance with Norlin Music (F.A.Reynolds horns)
1971	around 720,000	Zig Kanstul leaves Olds to take over Benge plant
1979	July 13th, approx. serial # A41000, production ceased
1979	1979,Nov. 7th all production equipment and parts were auctioned.At the auction Allied Supply purchased a 10 yr. supply of all parts (except bugles). Selmer/ Bach purchased tooling for all marching brass (not bugles) and large horns (i.e. baritones, tubas etc.). The trade names of Olds and Reynolds were sold to P.J. Laplaca Assoc, Ltd.