Serial number milestones

Larry Snyder wrote:

 But I do own A Touch of Class so I guess I can be!

I own the manuscript and it is not much help, a lot of what is in there was skimmed from other sources, I don't think he ever went to the source material.

I think a lot of what you are looking for can be found by comparing the information in the Type Certificate Data Sheet (TCDS) and some AD's and the production history report. The TCDS files are also available on the univair resources web site as well as the AD's.
Your example of looking for the change to the 6 gallon header tank is one. That change had to be approved by the FAA /CAA to be certified so it has to be included in the TCDS.
There are 2 TCDS files A-718 and A-787 for the Ercoupe, Alon etc aircraft. File A-718 has the fuel capacity of the early Ser # 415-C's as 14 gal , one 5 gal header and one 9 gal wing tank with optional changes to the wing tank configurations only. No notes or other references to the header tank were found.
TCDS File A-787 starts with the production of the first 415-D's ser # 4424 and 4435 then skips to 4501 with the first 415-CD. The fuel capacity is specified as 24 gal including a 6 gal header tank. I would conclude that this change to a 6 gal header started with ser# 4424 on 3/25/1947. The type certificate was not approved until 6/17/1947 but stated that specifications we effective on serial # 4424 and up for this type certificate.
Another example might be the following:
Apparently some early header tanks as well as wing tanks,  ser # 113 to 2468 ,were made with terneplate metal which began leaking over time. An AD (55-22-02) was issued to have them replaced with stainless or aluminum tanks if leaking but did not specify capacity. I would assume ser#'s after 2468 had a different metal for the fuel tanks used in production but we don't know what it was. At least we know there was a change on 7/18/1946 to the type metal used for production fuel tanks.
I hope this helps.
Thanks,
Robert Burdett  Ercoupe 415-C  N99369

I just came across this document that you may find interesting. However since I'm a relative new Ercoupe owner (1 1/2 years) you all may already have this information.
It's on Univair's resources web location.
www.resources.univair.com/docs/ercoupe-production-history
The document is a pdf of an excel spreadsheet that has serial number, registration number, Model with HP in (), date of manufacture, approximate date of manufacturer.
The pdf is sorted in serial number order. However it only covers 1940 to 1950 so it is only  the ERCO and Sanders aircraft. I hope this helps on a few of the things you were looking for.
Thanks,
Robert Burdett Ercoupe 415-C N99369

Love to know the serial numbers. Or N-numbers . Larry, u can add to the Split elevator