No. You can't. Free updates is locked to cars VIN and available only one time for this car. Mazdatools knows your VIN and expiration date. Doesn't matter what SD you will try to update your free subscription is already expired. The only way is to buy updates online for this car.The Nav SD card for my 2015 Mazda is out of free updates.
Can I just buy another card on eBay, which is cheaper than paying for updates, or is the update attached to the vehicle, not the card?
Your likely scenario is that the previous owner never installed the navigation SD card and that is why you were able to get the one you bought from ebay to work. If the previous owner had installed an SD and it was removed prior to you buying the car, you would be in the same boat. Mazda tools would know there was already a nav card locked to your VIN and you would have to purchase updates thru them.I don't see why not. I bought a used car that did not come with a Nav card, and purchased a new one on ebay with not issues.