I see a lot of variation over the year, sometimes as much as 5-10 degrees in the winter and shoulder months. Your grain temp, cooler temp, fitting temps, and basically anything that touches that wort can have more or less of an impact. Since you're doing mostly the same recipe, you probably don't have the problems I have, but I see a good bit of variance even in the amount of strike water vs. grain I'm using from recipe to recipe.
I spent quite a few brews (over 10) trying to train my system's results into software and eventually just threw my hands up and gave up with "close enough." I spent hours researching, adjusted almost every parameter in software that I could think of, took precise measurements of equipment temps, calibrated my equipment and so forth to try and dial it in precisely. Anymore, I just always aim a bit high and just a hair thin, using cold water to bring it down to temp with precision. (That's easier for me than raising temps.) Once I switched to this method, I was much happier with hitting my targets from batch to batch and can get/maintain temps to literally a half degree easily. I haven't had really any noticeable issues with a wee bit of time mashed high, so long as I work relatively quickly to get to desired temp.
In theory, all this stuff should be relatively predictable and the software does a decent job at estimating. But, it's still an estimate when it comes right down to it and there's a lot of variables in our systems and practices that can have an effect.
Good luck! That's just my method, others might have further insight.