Bridge Set Numerals? Curved Celluloid/Faux Tortoise

I picked these up years ago, ignorant of their origins. Thought perhaps they were warped by shrinkage of the tortoise layer. Today Google Lens offered an eBay listing for a Bridge Set in a case with Score Pads, etc, including a nearly identical 4 numerals; theirs had a dark background, but were the same 'Deco' font an' size (3" height), an' were similarly 'warped'. I know zip about the game or its accessories, but have hope that one of you folks can illuminate the purpose for these...an' why they are concave. Thanks for lookin'!