Even with established brands and a deep-pocketed backer, building a fashion group is not for the faint of heart.  Or the impatient. Lanvin Group has proved that once again, wracking up net losses of 263 million euros last year while revenues fell 18 percent to 240 million euros.  There were some signs of improvement at the parent company to Lanvin , Wolford, Sergio Rossi and St. John. Adjusted losses before interest, taxes, depreciation and amortization narrowed by 4 million euros to 90 million euros, reflecting a strategic reset that had the company closing 51 stores last year.  But it’s been pretty tough going.  All together, the group has accumulated losses of 976 million euros — 95 percent of which has piled up over five years.…