[Researcher]

It appears to me that most of the early .410-bore boxes and catalog listings don't mention how tiny the load really was.

1915-16 Catalog Small Gauge Loaded Shells.jpeg

2-inch .410-bore Remington Arms - Union Metallic Cartridge Co..jpg

.410-Bore No. 8 CH Shot.png

NITRO EXPRESS .410 2 1-2 inch 6CH.png

2-inch .410-bore.jpg

.410-bore High Velocity.jpg

The only boxes I've seen that admit to only 3/8 ounce is the early Western Super-X .410-bore --

SUPER-X .410 3-8 oz. 8 chilled shot 01.jpg