It’s an RCT. What will those measurements contribute? In addition, it is likely the measured serum levels will be lower because they are used up.
Here's a recent summary looking at both those papers and many others. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8787834/ TL;DR--it's all just too inconclusive at this point. Though as always everybody remains enthusiastic, notwithstanding that vitamin D papers have been perennial favorites long before COVID, without much to show for it.
FWIW, I think this is the retracted paper I had in mind earlier: https://retractionwatch.com/2021/02/19/widely-shared-vitamin... Somewhat similar design and at least one of the same authors. Retracted because it wasn't actually as randomized as claimed.