In the full filename, you might see something like allupgrade_aml920_4G_512M_mxl61_71.img . The "mxl61" part indicates the type of used by the board. The suffix "71" and similar numbers represent the duty cycle , a technical parameter related to the backlight current of the specific screen panel. The "None" in your search phrase likely indicates a user who either doesn't know or doesn't care about these specific model details.
Allupgrade AML920 4G/512M – No SOS / No Signal Issue Allupgrade Aml920 4g 512m None Sos-