Do you think my FUT surgeon made a mistake planning my grafts?

Surgeon got around 2980 via FUT. They were hoping for 3200-3300, but they were surprised to see the left hand side had 30% less density when the technicians were processing my strip. They said they would’ve planned differently on the right side to compensate for that falloff in density if they had known. Shouldnt they have known and anticipated this drop off in density if they had looked closely? Or can you be surprised by less density that you can only see when you cut the strip?