Demon diy carpet question

I’m replacing carpet in my 71 that I bought new. When I took it apart was the first I ever even noticed that it was two pieces. So there should be no worry about appearance.
As an aside, how did you guys determine where to trim it along the edges so it wasn’t too short or too much overlap? Thanks.
I work from the center outward. Keeping the side trimming for last. You can put the scuff moldings in place, after fitting the carpet, and mark where the plates go using chalk, then trim the carpet so it lands under the scuff plate. Get a bunch of single sided razor blades. They dull quickly on carpet. Do small cuts, working your way up to your marked lines.