How much liquid chlorine and acid have you added?
Evaporation and autofill should keep the level constant.
Water mixed well and sample taken from some location?
Using a speed stir, holding the reagent bottle perfectly vertical, allowing drops to fully form on tip (don't "force" them off), about 1 drop per second?
K-1766 testing is +/- 200ppm. So previous test was 3600 +/- 200 and current test is 4000 +/- 200. That would still put results within the testing margin.
Don't forget to add test kit info to signature.
While you should continue to monitor monthly (unless something seems wrong), as long as the SWG is happy and making chlorine, you are good.