Ouch

The smaller cleat might work, but it could wreck havoc on pedal adjustments, especially if you have a couple of different shoes that you use.

Actually, that cleat is missing enough features like the shoulders that kick the cleats out of the pedals that you should be able to recognize them, and avoid them. Could they have been brand specific such as MKS MM Cube cleats that are supposed to be similar to Shimano, but not quite?

Some Bike Co-ops will have spare cleats.
I've also purchased a pair of used shoes that didn't fit at a thrift store just to snag the cleats. I should throw them up on E-Bay (without the cleats) for a profit.