Spacing between extant fragments of 𝓞 suggests that Oliver Cowdery initially wrote “they did call on the Lord” in 𝓞, then supralinearly inserted the name of (or name of the). Elsewhere the text has examples of both phrases, “to call (up)on the Lord” and “to call (up)on the name of the Lord” (or equivalent examples involving God rather than the Lord ):
The King James Bible also shows similar instances with and without the phrase “the name of ”, as in the following contrastive pair:
There are also nine examples in the Book of Mormon text of “to call (up)on his (holy) name”. It is doubtful that Oliver Cowdery, the scribe in both 𝓞 and 𝓟, decided to consciously emend the text in Alma 19:16 by adding the phrase the name of to “they did call on the Lord” since he did it nowhere else in the text.
Summary: Maintain in Alma 19:16 the fuller reading “they did call on the name of the Lord”, the reading of the earliest extant textual source (namely, 𝓟); spacing between fragments of 𝓞 suggests that Oliver Cowdery initially wrote “they did call on the Lord” in 𝓞.