1 Nephi 13 attributes the loss to “the great and abominable church,” which LDS readers today usually take as a general apostate influence. Saying Joseph Smith blamed careless or corrupt transmission is a different claim.

Correct, and the two should be kept apart. The verse’s own attribution is to the great and abominable church, and LDS interpretation of that phrase ranges from a specific institution to a general apostate influence. Smith’s statement about ignorant translators, careless transcribers, or designing and corrupt priests comes from his teachings, not from 1 Nephi. Both describe a loss that predates every surviving manuscript, which is the claim the Reliability of Scripture case and this claim answer.