Quoted from erak:You never know if some "tech" decided it was a good idea to clean the playfield with paint thinner.
Then..... OOPS!
If you look at the blotches by the weapons targets, it looks like something was spilled on the playfield.
That was my thought. It's too clean overall to be wear. Probably applied something and forgot about it, and then wrecked it when it was cleaned off later. But I can't think of what would be in the typical Ops toolkit that would do this.