My MediaTek T-Mobile Velvet 5G has bands 13 and 71. I don't understand the harmonics issue either. It's solved on the transmitter side, right? If your IF receiver oscillator is 650 MHz to get 50 MHz from a 700 MHz signal, you wouldn't transmit anything at 600 MHz. Both already exist, so too late for that. Harmonics issues on phones is between digital circuits and the tuner.