Start sometimes goes much better, but usually you lose a lot of shields there, and I knew rest of the level can be done without serious damage, if it goes well, so I kept going anyway.
Well, I always play the level long enough to remember all robots, so I know exactly who is still in the map without even counting. The only level where I wasn't sure was L9. During the run there, I didn't know if I have killed all drones. In case I do some risky shots, where I don't see if the robot is destroyed - in this SL3 for example those smart missile shots to 3 quad laser guys, I quickly check the score to see if I get them all.
I'm always carefull about spiders to make sure there is no baby spider left. If needed, I check it in slow motion in replay before uploading the run. It would be a problem for example if you snipe spider from a bigger distance and then don't explore that place, but these things don't happen in any of my runs. So far the most problematic thing I have faced was matcen area before red key in level 23. I spent a lot of time studying behavior of robots there to be able to do it without wasting time by killing every robot. Anyway, it sometimes happen that I stupidly miss something or I think the robot is killed and actually isn't and I found it out while carefully going through the replay. If that happens I basicly play the level again.
There are 2 red hulks in reactor area. First one is killed by mega, second one is killed by overcharged fusion shot together with reactor.
Yes, that end can be cruel, I lost a run because of extra life in exit tunnel

. Taking it is in rules of "insmax" category.