A few years ago, an anonymous TIGHAR critic compiled a collection of photos and references describing ALCOA labeling on aircraft aluminum. It's at
https://aluminummarkings.wordpress.com.
In all cases prior to 1941, the labeling was "ALC24ST" other than "ALCLAD 24ST" as seen on 2-2-V-1. His/her conclusion was that the aluminum in the artifact was manufactured not earlier than 1941. (The current site begins "...precisely as the aluminum markings predicted. The artifact’s unique rivet pattern matches exactly the top of the wing of a surviving Douglas C-47B Skytrain built in the 1940s." We checked the wing in question in 2017. Not even close.)
Although the conclusion is bogus, it's an excellent collection of images What does it really tell us?
• The vast majority of photos date from after 1939. Why? Because aluminum aircraft manufacture prior to the outbreak of war in Europe was minuscule compared to wartime, beginning with British Lend-Lease contracts and the ramp-up in American military aircraft production. Pre-war photos of aluminum aircraft under construction are hard to find because there weren't many being built.
• With a single exception, all of the photos show labeling in the Stymie Bold serifed font. Boeing, Douglas, and Lockheed seem to have used aluminum manufactured at the Edgewater, NJ plant. 2-2-V-1 was made at the Alcoa, Tennessee plant.
• One photo (attached), taken some time between December 1942 and September 1945, shows female riveters working in an unidentified aircraft with aluminum labeled "ALCOA," the skin thickness, and "ANK" on one line, and "24S-T" on a separate line. The font is Gothic Title Medium. This appears to confirm two facts - 1. The New Kensington plant was using the Gothic Title Medium font prior to 1947, and 2. The New Kensington plant used wording different from the "ALC24ST" used by the Edgewater plant. Different plants sometimes used different wording.
• There are no photos inn the collection showing aluminum labeled with the Tennessee plant's Franklin Italic font seen on 2-2-V-1 and yet the plant's sheet aluminum mill had been in operation since 1919. The one photo we have of wartime production using Tennessee aluminum is the 1943 Consolidated PB2Y shown earlier in this thread. In 1943, Consolidated was using aluminum from the Alcoa, TN plant. The photo shows both the "ALC24ST" and "ALCLAD 24S-T" wording. Again, different plants sometimes used different wording.
We need more data. Consolidated built the PB2Y at its San Diego. PBYs and B-24s built in San Diego should also have aluminum labeled in the Franklin Italic font. The PBY-1 first flew in 1935. If we could find a photo showing labeling on an early PBY under construction, it might match the labeling we see on 2-2-V-1 and prove the artifact COULD date from 1937. It wouldn't prove the case, but it would eliminate a possible disqualifier.