Month names collection / metastudy

[RadioFM]

Exactly my thoughts. Even though modern day French (and Picard) seem to pronounce word-initial y exclusively with the "soft" /j/ sound whereas word-initial j with "harder" /ʒ/ (resp. /d͡ʒ/) sounds, I think it's certainly plausible for some medieval scribes to have abused the y=i interchangeability, extending it to word-initial positions as well, especially back then when orthography was far from standardized. Thus, /ʒɔ'lɛt/  /d͡ʒol'lɛt/ (or some variation in-between) could have been rendered iollet jollet or yollet, all three pronounced the same, unlike nowadays where yollet would definitely be read with a /j/ sound

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As an anecdotal sidenote, it's not unheard of of romance languages evolving different y consonant sounds. Even after having merged /y/ sounds into /i/ or /j/, Argentinian and Uruguayan Spanish accent have coincidentally evolved a /ʃ/ and /ʒ/ consonant sound for y while still keeping the /i/ and /ʝ/ (~ /j/) vowel sound. For instance, "yo soy" is pronounced  /ʝo soi/ in most Spanish-speaking regions. Standard Argentinian/Uruguay accent realizes it /ʃo soi/. This is most likely a funny coincidence and has no actual causal relation with the yollet/jollet question, but I thought I'd mention it for some plausibility of a hardened y sound