Supersedes:?[\r\n ]+[w-s]+[\r\n ]+(.*)[\r\n ]+Serial Numbers?:?[ \r\n]+.*?

import re
result = re.search('Supersedes:?[\r\n ]+[w-s]+[\r\n ]+(.*)[\r\n ]+Serial Numbers?:?[ \r\n]+.*?', 'rnrnSupersedesrnNonernrnTriax PFG Interface Boards: Inova: P/N 01-903510-02 and Unity plus: P/N 01-903510-03rnrnService Serial Numbers:rnUS00000000-US99999999rnrn', re.S|re.M)
result[1]
'Boards: Inova: P/N 01-903510-02 and Unity plus: P/N 01-903510-03rnrnService'