In Keilim 20:6, we see a disagreement between Beit Hillel and Beit Shammai (and Rabbi Akiva) as to when a floor mat (that is susceptible to midras impurity) loses its susceptibility to midras while being turned into a door curtain.
סָדִין שֶׁהוּא טְמֵא מִדְרָס וַעֲשָׂאוֹ וִילוֹן, טָהוֹר מִן הַמִּדְרָס, אֲבָל טָמֵא טְמֵא מֵת. מֵאֵימָתַי הִיא טָהֳרָתוֹ. בֵּית שַׁמַּאי אוֹמְרִים, מִשֶּׁיִּתָּבֵר. בֵּית הִלֵּל אוֹמְרִים, מִשֶּׁיִּקָּשֵׁר. רַבִּי עֲקִיבָא אוֹמֵר, מִשֶּׁיִּקָּבֵעַ:
If a sheet that was susceptible to midras uncleanness made into a curtain, it becomes clean from midras uncleanness but it is still susceptible to corpse uncleanness. When does it become insusceptible to [midras] uncleanness? Bet Shammai says: when the loops have been tied to it. . Bet Hillel says: when it has been attached. Rabbi Akiva says: when it has been fixed. [from Sefaria]
Beit Hillel's opinion is that the mat is still susceptible to midras at a time when Beit Shammai's opinion holds is insusceptible (namely, when loops are tied to it, but it's not yet hung up). Why isn't this listed in Masechet Eduyot amongst the other places where Beit Hillel is more stringent than Beit Hillel (see Eduyot chapters 4 and 5)?
I know that there are other understandings of this mishnah, but I'm asking according to the understanding (presented as the first option in Kehati's commentary) that Beit Shammai requires just attaching loops (and not a major alteration like ripping and resewing).