seofontigoþa [OE]
seventithe [MI]
seventieth [ME]
seventieþ
https://www.etymonline.com/word/seventieth#etymonline_v_48735
https://www.merriam-webster.com/dictionary/seventieth
https://quod.lib.umich.edu/m/middle-english-dictionary/dictionary/MED39695
https://bosworthtoller.com/53369