Yeah this is one of those things that once you see it you notice it everywhere. Like how a "quarter pounder" weighs less after cooking, or how a 16 oz bottle of juice is actually 15.2 oz if you read the fine print. The lumber thing is just nominal sizing, meaning the name is a label, not a real measurement, and it's been that way for like a hundred years because they dry and plane the wood down after the rough cut. For cut lists I just always work off the actual dimensions, so a 2x4 is 1.5 x 3.5 and a 1x6 is .75 x 5.5, and I add a little slack on length since the ends are often rough too.

The check made it harder? Just cash it.

I used to do something kind of the same but backwards. I'd save all my admin stuff for the last hour of the day and tell myself it was "reward time" for finishing real work. Worked great until I started blowing it off because I was tired and just wanted to go home. Turns out a tired brain will find any excuse to skip invoicing. So yeah, front loading it like you're doing makes way more sense than my dumb little system.