I have #621 built on December 17th, 2015 and it has the insert issue. I haven't heard of one in the 600's that hasn't been affected. Of course there may be one off special request numbers in the 600's that may be fine as long as they were made in one of the earlier batches of MMRs. Also, the black will look fine when it is off so if the seller sends you pics, make sure he turns it on. In all honesty though, i think most of these affected playfields are legible. They are just not as nice of a solid black as the earlier runs. I can read all of my inserts fine when lit, but they are not like the solid black I have seen on earlier runs.