Still you are confusing different issues.
1) "DVB frequency finder" creates a providers file. That providers file lists all the strongest unique muxes where the frequency of the mux in "SDT actual" does not correspond with the tuned frequency or where the SI tables do not list a frequency for that mux. It also adds the strongest DVB-T mux as the home transponder. When ABM uses this file it substitutes any "wrong" or missing frequency in the SI tables with the correct one from the providers file. Previously this operation was laborious manual process but now it is handled automatically by "DVB frequency finder".
2) Because ABM produces its result by reading just one mux there is no way to know whether all the muxes listed in the SI tables are within the reception scope of the hardware.
3) Neither "DVB frequency finder" nor ABM creates terrestrial.xml files.
4) If you want a custom terrestrial.xml use the TerrestrialScan plugin. The output to file will be the strongest unique muxes. i.e. there will not be duplicate entries if identical muxes are found.
5) Because TerrestriaScan does an exhaustive search, all saved muxes are known to be active at the time of the scan.