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If this works it can actually be a cheap easy method. Umpires just need a ruler. Even the opposing player can check.but we don't know where this safety label should be applied, on the rubber or the sponge ? because if it's the rubber, of course when boostering it stretches, so yeah if the SL is then too large according to a standard that has been decided in the ITTF laws, then it should avoid couterfeiting by boostering, but I'm only making assumptions here...
If one knows the distance between sponge pips of each rubber as manufactured, you can calculate if the rubber has been stretched?