I don't know if Fitch is an off shoot of Madonna. But I don't think they ever shared code prefix. All the JUFD- vids in my database says Fitch, not Madonna. Fitch used these prefixes: FINH-, JUFD-, JUFE-. JUFE- is the current prefix.
Between JUKD-, JUC-, JUX-, JUY- and JUL- these are all Madonna prefixes: JUKD- around 2006, JUC- around 2010, JUX- started around 2013, JUY- started around 2016, JUL- started around 2019. JUL- is the current prefix. There's no difference between these prefix other than time. Over time, of course any label or studio would drift in style and feel.
When one prefix is exhausted, up to -999 but not always. Then the next one starts at -001. Another example is S1, they had, in chronological order: SOE-, SNIS-, SSNI-, SSIS-, which is current. (not exhaustive)
Many studios also has a different prefix for compilation vids. Like OFJE- for S1, MIZD- for Moodyz...
Some studios has a huge range of prefixes for their different labels: Moodyz has: MIDE- (exclusive), MIAA- (kikatan), MIMK- (hentai), MIRD- (Real = grand orgy)
SOD has even more: STARS- (exclusive), SDNM- (MILF), SDAB- (young/loli), MSFH- (fresh face), SDDE- (fantasy planning???), SDMU- (magic mirror bus?), KMHRS- (???), KIRE- (???)