Sam2: I hope I can explain it as well as my husband explained it to me. No one person can possibly fulfill all 613 mitzvot by oneself. Some mitzvot are meant for men, some for women, some for converts, etc.. There is a shlaimus we achieve through keeping the mitzvot. When Yaakov said ‘im Lavan garti’ (meaning that he kept the Taryag mitzvot) he was saying that he had achieved the same shleimus as if he had kept the full 613. He achieved whatever level can be attained through fulfilling the mitzvot. He did not actually follow the pshat of all 613 of the mitzvot (which is impossible in any case) but he was as complete of a person as if he had.
My husband explained with more sources but I’m not so learned so I’m repeating what i remember from what he said.