We thought the tyre doping book was closed after Jared Mees was found guilty of having a tyre that Dunlop concluded had been chemically altered, at Atlanta 2018 (see Mees Disqualified post), but it seems at least one rider thought it was worth a try.
Californian Production Twins, Michael Inderbitzen #54, has been found quilty of racing with a non-compliant tyre at last month's Black Hills Half-Mile. See the screengrab above. He had his points deducted. It must make quite a difference if people are still trying it, knowing the penalties of being caught.
Incidentally, we were told that as soon as the news broke about Mees being disqualified, Dunlop sold out of race tyres. Draw your own conclusions, but the inference is lots of other riders needs to get 'clean' tyres on their bikes before the next round of testing.