Here in verse 29 the text is referring to numerous futile attempts on the part of the Lamanites to surround and attack the Nephites at night. As explained earlier in the passage, the Nephites had already taken many Lamanites as prisoners; we have, for instance, the following statement in verse 27: “and it came to pass that they did—notwithstanding all the intrigues of the Lamanites— keep and protect all the prisoners which they had taken”.
David Eddington (personal communication, 23 October 2003) points out that what the text literally says in verse 29 seems odd, namely, that the Lamanites lost many prisoners when they wouldn’t have been prisoners until they had been captured. One could propose here that an original essive as is missing: “but in these attempts they did lose many as prisoners”. There is some evidence in the next chapter of Alma for this usage:
But usage also shows that in many instances the plural noun prisoners lacks the as that modern English readers might expect:
The critical text will therefore maintain in Alma 55:29 and elsewhere in the text the original instances of prisoners for which the essive as is lacking (that is, without the as that modern English readers expect).
Summary: Retain in Alma 55:29 the original reading without any as before prisoners (“in these attempts they did lose many prisoners”); this kind of essive usage without as can be found elsewhere in the text.