I agree Cat pee! Rich won't believe anything else so I fully agree!!!!!
I already told him it was glue.

Lead weights cause those round circles as it expanded, or was made raised (not 100% sure how so won't say), when made.
Glue was also used on chips to hold the inlays in on most chips I have seen that have come apart & that is not many but enough to know glue was used. Glue somehow soaked through the paper & as some will know old glue can change color like tape. That is the problem.

OR is it cigarette burns from smoking workers ashes that dropped on the chip & were laminated over???
Ha Ha.