Here in the printer’s manuscript, Oliver Cowdery initially wrote Zenith, an English word, in place of Zeniff. Later he overwrote the th with ff; his correction to Zenith is with heavier ink flow. This is the third occurrence of the name in the text; all others are spelled Zeniff without variation. Oliver’s correction here in 𝓟 could be the result of either editing or proofing 𝓟 against 𝓞, no longer extant here.
Summary: Maintain the spelling Zeniff throughout the text; the initial occurrence of Zenith in Mosiah 7:21 was a simple scribal error.