Is it permissible to adopt the fatwa of other madhhabs regarding the emission of madhy (pre-seminal fluid) for a fasting person, and is what the questioner did—making up the days in previous Ramadans during which madhy was emitted—correct?

The emission of madhy (pre-seminal fluid) does not invalidate the fast unless it is due to customary pleasure. If it is emitted without pleasure, or with non-customary pleasure, it does not invalidate the fast according to the Malikis, and this is the preferred opinion among many scholars.