Your buddy has it backwards. Paperwork is the first thing to lie in a house that's been flipped or DIY'd, and a taped-in panel schedule is just a note somebody scribbled years ago. The copper doesn't lie, and neither does a clamp meter. If the wire is 14 gauge, that's a 15A circuit no matter what the label or the breaker says, because the breaker only protects the wire. What gets people hurt is trusting a label and stuffing a 20A breaker on 14 gauge wire, and now the wire is the fuse. I would've done the same thing you did, new home run from an open slot, and then written the true wire size and amp rating on a fresh label so the next guy isn't standing there scratching his head. Document the mismatch in your invoice too, so it's on record. A schedule is a hint at best, the meter and the gauge are the truth.

That line about turning into a subscription they forget to cancel is painfully true. I had a client once keep paying a small monthly fee for eight months just because I fixed their email signature in April and they figured I might be useful later. Pitching it to hourly folks is rough though, the ones who bill by the clock hear "retainer" and picture a gym contract they can never escape.