A few errors i noticed in DBZ?

ok like when goku and gohan are in the hyperboylic time chamber and goku is like just picture cell terrorizing the people you love and let your rage burst out and gohan responds but ive never seen cell. but later on while training inside the chamber gohan invisions cell killing all of his friends and trys to go super sayin. another error is when trunks and krillin found the extra time machine and cell said he had come from 24 years in the future and that he had killed trunks with ease taking the chamber because trunks had already killed the androids in that time. well he said it was easy to destroy trunks but how could that have been possible he was in imperfect form and trunks had come back from the past and had already trained in the chamber. also he said when he came back he all he had to do was push a on because the location and time were already set. ok so how did he end up in the time 1 year before the reguler trunks even shows up in the reguler series i mean the trunks that