Back of the plane

Sky and I looked online to see if we could find out where we would be seated on each flight. Usually in one of the rows near the back. That must be the safest part of the plane? Unfortunately, we couldn't identify the exact seats except for the Vancouver-Beijing flight pictured here, where our seats are marked in red. In the other seating charts, we always seemed to be in seats like 52L, and the seating goes alphabetically from A-K... Sky thought it meant we got the spaces marked "L" on the seating charts near the front and back of the plane, not knowing L stands for "lavatory".