When Oliver Cowdery copied the text from 𝓞 into 𝓟, his eye apparently skipped down to the following line and he initially copied “& supposeing” (rather than the correct “had supposed”) from the immediately following line in 𝓞. The transcript for this part of 𝓞 shows that the first instance of the verb suppose would have been almost right above the second one:
Oliver soon corrected his error in 𝓟 by crossing out “& supposeing” and supralinearly inserting “had supposed”. Oliver’s correction in 𝓟 was probably later (perhaps when he proofed 𝓟 against 𝓞) since the ink flow for the had is somewhat heavier and for the supposed slightly heavier.
It is worth noting that the original text here could have read with both instances of the present participial supposing but with only the second and:
But the fact that Oliver Cowdery initially wrote “& supposeing” in 𝓟 argues that this and was secondary and that its source was the following “& supposeing”. The critical text will assume that the initial “& supposeing” was a simple copying error and will maintain the corrected reading in 𝓟, “had supposed”.
Summary: Retain in Alma 58:25 the corrected reading in 𝓟: “for the chief captains of the Lamanites had supposed that the Nephites were weary because of their march”.