Yoox Top Brands Sale up to extra 90% off!这个extra是指折上折？？

fs首页上贴出来的,最高的折扣有91% off，
Yoox Top Brands Sale up to extra 90% off!

它自家首页只写了spring-summer sale to extra 40% off
这个extra是指折上折？？

图里的STELLA McCARTNEY 3/4 length skirts是90% off