The valuation is rebuilt from scratch each month

Every month the valuation starts at zero: walk the job to guess what moved, hunt the inbox for evidence, rebuild the variations position from whatever surfaces, and get the number out in time for the application. It costs days, and it drifts with whoever assembles it, because a build-up leaning on memory produces a slightly different job each month.

A valuation drawn from a kept file is a different kind of document: progress from the site capture, change from the register, this month's movement measured on top of last month's agreed base. It takes hours rather than days, and more importantly it holds, because when a line is questioned the trail behind it exists: the photo, the instruction, the measure. The valuation stops being an opinion with a deadline and becomes a record with a total.