...especially diecast, as a LOT of things are not what they are claimed to be.
-ALL Jo-Han AMC kits from 1961 on are 1/24 scale. The promo boxes confirm this, as do basic dimensions like wheelbase and overall length.
-The Jo-Han '62 Studebakers are closer to 1/23. Larks were midsize cars at best.
-The ex-IMC Dodge D-100 is closer to 1/26 than 1/25. Jimmy Flintstone sells Ford Econoline van and pickup bodies that appear to be cribbed from a diecast, and are sold with the intention of using the Dodge chassis and floor. When one of the Econoline bodies arrived, I checked the wheelbase (should be 90", same as the Dodge). I found it underscale, and was thinking about how to correct it. Then I measured the Dodge kit body, and found it equally undersize.
-A lot of the early promo-based kits of bigger cars like Imperials, Cadillacs, and Continentals are undersize. How did AMT get away with using the exact same tires on both a late Sixties Ford Falcon and Lincoln Continental?