They are from different runs and different art. I looked through a rack and found roughly half and half like Michaels.
On the chip with bigger inlay, the word 'Stratosphere' is a full 2mm wider than on the smaller inlay. There are a number of minute differences on the design and the 'LAS VEGAS' is in a different font
That said, this is probably a common occurrence for a casino that probably gets through a gazillion of $1 chips a year. Call it a variation if you must but it would not warrant a separate catalog listing.