I recently sold my buds on eBay. Both working when sold. Buyer claimed the left bud didn’t work so wanted to return them. Already had my suspicions but when returned as gross as this is the right was clean as sent and the left had wax in the rubber. I decided to open them up to see if they had any serial numbers inside. On doing so the date on the circuit boards are different and one is white and one is black. Should they both be the same colour (thinking they could be different colours for left and right) and should the dates match. Starting to think they had a set already which was faulty and they have replaced the faulty bud with mine to make a good working pair.