Yes, if every option was possible then we could get 1, 2, 3, 12, 123, 13, and 23. Most of the time, not every option does happen, some of these options would require multiple distinct promoters or some other features such as alternative polyadenylation to occur. However, it is theoretically possible and in places like the immune system it is not uncommon for loads of different variants to be produced from one gene. The dogma of one gene = one protein is firmly dead.
During protein translation, which molecule carries the amino acids to the ribosome for assembly into a polypeptide chain?
LaNts and Laminins 