If there is a certain concept, that you dont understand and would like to attend another lecture again to listen to it please go check with ur lecturer. I am sure he/she knows which lecture to slot you in or can explain to you on the spot. Crashing lecture on such circumstance, I can understand, since it doesnt happen often.
But constantly crashing other ppl lecturer is a pain in the a**, esp those popular ones. You totally deprive reg student of a seat, delay class from starting because students cannot find a seat, and make the lecturer call the admin to weed out illegal students. It just totally spoils one mood of learning. Btw it happens to my audit class rather often, until ms chu also pissed off.
As for the notes, i think enough others have said enough.