The Five Brothers Shirt which I was gifted when I was down on my luck and just out of the service was made in a quantity which allowed a friend's aunt to purchase 4 of them as gifts for all the younger folks at her Christmas party that year, and there were quite a few on the sales floor at Sears when my folks took me school clothes shopping each year.

They are still in business, but I wonder what changed when the last time I looked at their shirts, they were north of $150, and now they are quite competitive in price, and I worry about the quality as is being debated in this thread.

Still have that shirt, four decades later, and still wear it around the house, though it's a bit frayed from rough work chopping and hauling firewood when I was younger.

OP mention shirts from the 30s-50s. I’m sure the operation warehoused more as the market changed, but I wouldn’t be surprised if some of the garments 100 years ago were basically made to order for a mail order taking a week or more to deliver. I’d expect by the 80s this had entirely changed.