seofontig [OE]
seventi [MI]
seventy [ME]
https://www.etymonline.com/word/seventy#etymonline_v_23301
https://www.merriam-webster.com/dictionary/seventy
https://quod.lib.umich.edu/m/middle-english-dictionary/dictionary/MED39693
https://bosworthtoller.com/19945