Most references cite about 10% of messages partially (or sometimes completely) decrypted prior to 1 December 1941, at which time a new edition of the system went into effect and sent all the cryptanalysts back to the beginning.
mˈoʊst ɹˈɛfɹənsᵻz sˈaɪt ɐbˌaʊt tˈɛn pɚsˈɛnt ʌv mˈɛsɪdʒᵻz pˈɑːɹʃəli ɔːɹ sˈʌmtaɪmz kəmplˈiːtli dᵻkɹˈɪptᵻd pɹˈaɪɚ tə wˈʌn dᵻsˈɛmbɚ nˈaɪntiːnhˈʌndɹɪd fˈoːɹɾi wˈʌn, æt wˌɪtʃ tˈaɪm ɐ nˈuː ᵻdˈɪʃən ʌvðə sˈɪstəm wɛnt ˌɪntʊ ɪfˈɛkt ænd sˈɛnt ˈɔːl ðə kɹɪptˈænɐlˌɪsts bˈæk tə ðə bɪɡˈɪnɪŋ.