What happens if one forgot to do an actual bedika for hefsek tahora, yet one still managed to do moch dachuk ?
When a bedika is made, it has to be done in a way that insures that all the crevices are also clean. There is controversy if b’dieved we can say that since the moch was there for a while, that it managed to get into the crevices, and it is b’dieved ok, or not. This can happen when a woman does a hefsek tahara, and it looks questionable, when she does the moch, she should turn it around, so that just in case the hefsek wasn’t good, the moch can be considered a hefsek. Due to this controversy, the best thing is that whenever a moch is inserted, it should be turned around in a way that it also gets into the crevices, and then it would be alright.
Shiurei Shevet Halevi 196-1 (13), Teshuvos V’hanhagos 1-508 (15), Mareh Kohen pg. 49, Pischei Halacha vol 2 pg. 161, 186, rule stringently on this. However in The laws of Nidda (R’ Eider) 1 chp. 3 ftnt. 106 in the name of R; Moshe Feinstein zt”l, Emek halacha 6-439, Livushei Oz 196-1, permit it bdieved. Shoshanas Yisroel chap.t 46 ftnt. 269, (that it is permitted if she walks around while it is inside, because then it gets pushed into the crevices), Zera Shmuel ftnt. 397, Maayan Omer 7-chap.1 164, Chut Shani 196-4 says that it is permitted in conjunction to other factors.