Credit transfer

hello guys,

i am doing now my exam application on ecfmg site to register to step 1.
i read about credit transfer and from what i have understood, we have to mention about every medical institution in which we have studied.
i have studied in two different universities and made also an'exchange program in another university, is that means that i have studied in 3 different places ??
and if its so will ecfmg need to verify my credentials in the 3 universities ??

thanks for your answers