Сибирская кошка и невская маскарадная - разные породы. Вот здесь почитайте историю возникновения невских маскарадных: http://www.sib-cats.com/%D1%80%D1%83%D1%81%D1%81%D0%BA%D0%B8%D0%B9/%D0%BE-%D0%BF%D0%BE%D1%80%D0%BE%D0%B4%D0%B5/%D1%81%D0%B8%D0%B1%D0%B8%D1%80%D1%81%D0%BA%D0%B0%D1%8F-%D0%BF%D0%BE%D1%80%D0%BE%D0%B4%D0%B0-%D0%B8-%D0%BD%D0%B5%D0%B2%D1%81%D0%BA%D0%B0%D1%8F-%D0%BC%D0%B0%D1%81%D0%BA%D0%B0%D1%80%D0%B0%D0%B4%D0%BD%D0%B0%D1%8F-%D0%BA%D0%BE%D1%88%D0%BA%D0%B0-%D0%BA%D0%B0%D0%BA-%D1%8D%D1%82%D0%BE-%D0%B1%D1%8B%D0%BB%D0%BE/