Almost every disagreement about numbers in the Quran comes down to four decisions made before anyone starts counting.
The text is fixed; the verse boundaries are not. Kufan numbering gives 6,236 verses and is what the Madinah mushaf prints. Basran, Medinan, Meccan and Syrian schools count between 6,204 and 6,232. Any claim that hinges on a verse number inherits this choice.
Only in Al-Fatihah is "In the name of God" numbered as a verse. Elsewhere it opens the surah unnumbered. Word and letter totals move by hundreds depending on whether the 112 unnumbered basmalahs are included.
The Uthmani script drops some long vowels that modern spelling writes out (for example الرحمن has no alif after the mim). Letter counts differ by spelling. Letter-based claims, including most of the "19" claims, are sensitive to this.
Counting "day" can mean the exact form يوم, that form with any prefix, every singular variant, or every word from the root. Each gives a different total. The balanced pairs on this page nearly all rest on one such choice, which is why they are marked "depends on counting".