The "How To" section gives this advice on control lines:

At this point once two marks are set and line snapped on the subfloor. Measure for square ness from the new line to wall # 2 and 3. If all the parallel areas look square there will be no need to adjust anything; simply start your installation from wall #1.

However, it does not say what you should adjust if walls in a room are not square. Clearly if this is the case one part of your floor will converge into the wall before the other and would require you to cut your final boards at an angle. Another possibility would be start the floor off square with the starting wall. For example if you are 1" off in a 10' room starting 1/2 off and ending 1/2" off would split the divergence on both sides of the room possibly covering the flaw to the n-aked eye.

What’s the guidance for making adjustments around control lines?

Thanks,

--David

Unsure of your question. Your concept of splitting the difference is sound and what would normally be done. So, if the room was 1" out of square and you wanted to "split the difference", one simply would add 1/2" to the mark on the subfloor on the end were the room was wider. Example: You're installing a 3" T&G plank with the tongue protruding 1/4" from the face of the 3" board. To mark the subfloor normally, you would add 1/2" for the expansion and 1/4" for the tongue protrusion, making your mark 3 and 3/4" off the wall. This is for lining up the boards tongues with the chalked line. Now on the end that is wider, you would add 1/2 the difference of the total room width. If the room were 10' across on one side and 10'1" on the other side, then 1/2 the difference is 1/2". Add that amount to the subfloor mark on the end that is wider, for a total of 4 & 1/4". But since you're using 3" planks, you need to reduce that measurement so you do not have to install thin pieces. So, on the wider 10' 1" side, mark the subfloor the 3 and 3/4"; and on the narrower 10' side, subtract 1/2" and mark it at 3 & 1/4". Snap with a chalk line those two marks. Then you'll need to rip down most of the starting course to fit to your starting line. But you will not have a bunch of slivers to install. Since the max width of the room is 10' 1" and we're using a 1/2" expansion space on each wall, you should end up with full boards starting and ending on the wider 10' 1" side and a tapered rip to 1/2" ( on each wall ) on the narrower 10' side.