How do you know it's this store's store brand?

Casual Male has always been my clothier of last resort due to their prices and odd locations but a few months back when I purchased a shirt under considerable duress they were the only game in town.  Shortly after purchasing the shirt developed a very clear rip along the seaming of the shoulder, something very difficult to due unless you’re going Bruce Banner on the damn thing.  I attempted to return it for a replacement today and was rebuffed when I couldn’t prove it was from Casual Male:
Me: But it’s from your store
Him: I’m sorry, sir.  But without a receipt we’re not certain it didn’t come from another retailer
Me: Inner Harbor is a private label brand, it’s only sold by Casual Male.
Him: I don’t believe that’s the case, sir.  Many of brands can be found in other retailers at considerably higher brands
Me: Yes, maybe Izod, Hugo Boss, Dockers are but Inner Harbor is only found in Casual Male.
Him: The only way I could verify that is if it the item says Casual Male on it.
Me: It does! It’s Inner Harbor… *sigh, leave with head down sulking in the rain*Because we all know how more of Route 66 jeans would be sold if instead of the embossed leather hind-panel instead they had a big fuckin’ plastic K stapled to the back pocket that said “For Trailer Trash, by Trailer Trash” or if Aldi’s Olympia brand instead said “Aldi’s, we’re European, biotch!”