'There is no formal tail dragger endorsement'....not correct, there is. Under JAR/EASA differences training is required for, amongst other things, tailwheels. The format required is 'ground instruction in appropriate training device and/or flight training, as required to exercise the difference'. Can be done by a CRI or FI, signature & license number required in logbook. TMG flying with a tailwheel will count; get the instructor to sign off your tailwheel differences training.