Here we have two passages in which the phrase “a lost and a fallen people” occurs with repetition of the indefinite article a. We see in both of these examples the natural tendency to accidentally omit the repeated a. In the first case, the 1905 LDS edition dropped the repeated a, but it was restored to the LDS text in the 1920 edition; in the second case, the 1840 edition dropped the a, and the RLDS textual tradition followed that reading until the a was restored to the RLDS text in the 1908 edition.
There is one more instance in the original text of “a lost and a fallen people”, and it too has suffered the loss of the repeated a, in this case in the 1852 LDS edition:
In this instance, the LDS text has not restored the missing a. The critical text will maintain, of course, all three instances of the original phraseology, “a lost and a fallen people”. For further discussion, see under conjunctive repetition in volume 3.
Summary: Maintain the three original instances of the phraseology “a lost and a fallen people” in the text (in Alma 9:30, Alma 9:32, and Alma 12:22); the repetition of the indefinite article a for conjoined nouns is common in the original text and will be maintained wherever it is supported by the earliest textual sources.