Dear secretagent,
Yesterday I wrote a long explanation about the relationship between that Tosfos and the Black plague, and also about Rashi on Ta’anis and Chachmei Magentza. Then they found the boys, the computer was taken over by the news, and my comments were not saved. I and many others will be at the heartbreaking levayahs today, and I don’t have the koyach today to reconstruct what I wrote. But I will, eventually.
To save yourself time, if you can get a hold of Ohrbach’s masterpiece “Ba’alei Hatosafot” and Grossman’s masterpiece “Chachmei Tzarfat Harishonim”, what I have to say is taken straight out of there.