This is interesting...as mentioned already...the part database only shows one level sensor. I pulled up the f01, f13, and f10 just to check several BMW models of the same era to see if the part nbr database was the same...all the models I checked (750i/M6/535i) all only had one fuel level sensor.
Then I checked the TIS...and it does mention that depending on specific models...there may only be one fuel level sensor...and then some have a "fuel level sensor 2". Then they use an F01 tank as an example showing the location of the 2nd fuel level sensor:
