Some rabbis from around that era (most called Yosef, interestingly) claimed women need not cover their hair at all, period. Then-modern “Modern Orthodoxy”, with which Rabbi Soloveitchik is partly-correctly associated was lax in various halachos, especially Tznius, of course (things have changed for the better). Nevertheless, Rabbi J.B. Soloveitchik explicitly held, as do virtually all Poskim, married women must cover their hair in Reshus Harabbim.
I saw this in “Conversations With the Rav” p. 114, עיין שם. The author notes the same is recorded in Rabbi Hershel Schachter’s “Nefesh Harav” p. 255 (I don’t have the book).