How can I debrand my AT&T w580i?

[MMan]

you can debrand it you need xs++3.1 a main firmware in .mbn format fs(filesystem) firmware in .fbn format and a custpack,
see here

Now see, I'm confused. I initially debranded my Att w580 with Wotan. Then because Wotan didn't have R8BA024 available, I used Setool2lite to reflash again. Then not happy (sue me, I'm compulsive) with the Asia firmware that I used with Setool2lite, I came here and used XS++ to flash W580_R8BA024_FS_AMERICA_1_RED52.fbn and the Laura_i_CDA102774_20_R1A_Generic_Trade_USA.zip custpack. Everything worked great.

My question is, why did I not need a main file to go with the .fbn file? (Not that I saw one to use anywhere) Thanks.