In this passage there are two instances of “the greatest number”. In the first case, Oliver Cowdery initially wrote “the largest” in 𝓞; then he erased largest, overwrote it with great, and continued inline with the superlative ending est. Clearly, the correction was immediate. Since either reading is possible, the corrected reading is undoubtedly the original reading.
In general, the text allows for number to be modified by the adjective large but only in its uninflected form; on the other hand, number can be modified by the adjective great in its comparative and superlative forms as well as in its uninflected base form:
The critical text will therefore maintain the two occurrences of “the greatest number” in Alma 24:28.
Summary: Accept in Alma 24:28 Oliver Cowdery’s immediately corrected reading in 𝓞 of “the greatest number”; here Oliver initially wrote “the largest number”, a reading that is unsupported by usage elsewhere in the text.