It is extremely common to find sheets from other cars in the seats, however the trim code will always be the same. The sheet was used to schedule a specific seat cover to be wrapped on a seat frame, and once that task was complete, that piece of paper became obsolete. In many cases the sheet is completely hidden once the seat is complete. I have found up to four sheets in one car, one for each section of front and rear seat. Sometimes all are a match, sometimes only one is a match, and sometimes none are a match!

My maroon chevy II had a sheet in the passenger seat 10 numbers before mine same color interior.My fawn car had a butternut yellow sheet in it same black gut car.