Where, I couldn't find it.
i don't remember what volume it was from. however, Schierke (or however the f0ck you spell her name) flat out said that the only reason Guts was able to injure Slan's body was because his sword has aquired magical powers after slaying so many demonic creatures. look for the issues after Guts/Slan fight.
as for physical damage, yeah, Slan was hurt by it but only her physical form. the original Slan wasn't. difference. she can take any form she likes and at this point she took her form from the flesh of dead ogres. you can't compare her damage soak to that of beings whose body she used to appear. get real.
which is interesting when you think about it: not only can the godhands NOT be injured by regular weapons (which negates your earlier comment on how Griffith needed to avoid Gut's attack. he clearly didn't and was just showing off as was obvious from the entire dialogue. he flat out called Guts "useless"😉 but the few weapons that can injure them, injure only their phsyical bodies as oppossed to their true form.
Skull Knight is like 1000 years old and he's been fighting them for a lot longer. Guts has only fought them for 3 years and his blade was able to get magical powers...what do you think someone who's been doing it for 1000 years would be like? besides, he uses a magical sword which gets its powers FROM the behelit which is something that godhand themselves created. in other words, he's simply using their power against them because the behelit is all about bending the human dimension with the demonic one.
as for Griffith not being able to crush SK, again, SK can bend dimensions. at the time he was already escaping the dimension so he was in the phsyical one and beyond the realm griffith was in.