I find the seatmaps generally quite accurate, it's when the 2 777-200ERs on trips to SIN over the past year, with the flights picked specifically for 777-200ER since I haven't been on one yet, turned into an 747-300 there and an AB6 back
(Oh, they were in C by the way, just to really cheese-me off.)

I knew then just exactly where I wanted to insert my rolled up seat map diagram that had been lovingly prepared !!! (enlarged, printed out, notes I wanted to make/confirm).