You said you've used wheelcalc in the past, so wheelcalc calculations will be consistent, since the same math is used every time. I explained how various calculators tweak or don't tweak results with correction factors (opinion of the programmer) for cross, on-center vs. inside elbow, or even some nipple height assumptions.

But the same calculator will give the same results for the same data every time, and will give consistent results for any set of data. It's a calculator, it runs the same formula based on the info you feed it, and doesn't have moods or whims. Of course if you're depending on it's internal database for dimensional data such as ERD, that's always subject to a data error in the database, or the rim's spec change over time (not that uncommon).

If you used the same program in the past and want to know where it (you) went wrong, re-enter the data set for the wheels, and if you get the same wrong answer, check the data against the actual measurements. Also take a moment to measure that the spokes are the lengths you think they are.

Of course, you can skip that and assume the calculator has some random whims programmed, or caught a cold.