If this was the case then it cannot be the case that this was a new idea to English speaking classicists because typically the third language they would learn i

If this was the case then it cannot be the case that this was a new idea to English speaking classicists because typically the third language they would learn is German. This is because so much 19th century classical philology was done in German (Nietzsche was of course a classicist before he was anything else and I've always thought that his attitude to Christianity was, at least aesthetically, not so much radically new as radically old). Milman Perry actually wrote his original thesis in French under Meillet and knew all the Annales crowd very well from his time in Paris. Meillet was himself a scholar of Slavic languages. It is the case that these ideas didn't just come from nowhere, Düntzer is important here along with other German speaking experts on orality and the metrics of poetry and Matija Murko along with many other scholars of oral South Slavic poetry. I'm not an expert but I've always understood that the consensus on Parry's contribution was that he developed not the idea about how oral poetry differs from written poetry when compared side by side but on developing techniques to detect the traces of previous oral traditions in poetry that was now exclusively written. In some ways, the only really sui generis contributions of Perry and Lord which are not part of a larger tradition and the importance of which should not be underestimated is the vast collection of recordings of South Slavic oral epic poetry. There was narrow window where that was possible, any earlier and the recording technology didn't exist. Any later and that culture was completely disrupted. Obviously there remain South Slavic oral poetry traditions but something like that doesn't make it through universal literacy, radio, and television unchanged and all of those came rapidly to the Balkans in the period immediately after.