diff --git a/R/aFIPC.R b/R/aFIPC.R
index 62546519..c8bdc58a 100644
--- a/R/aFIPC.R
+++ b/R/aFIPC.R
@@ -770,8 +770,8 @@ autoFIPC <-
       if (
         !is.na(newFormItemName) &&
         !is.na(oldFormItemName) &&
-          (length(stats::na.omit(unique(newFormModel@Data$data[, newFormItemName]))) ==
-            length(stats::na.omit(unique(oldFormModel@Data$data[, oldFormItemName]))))
+          (sum(!is.na(unique(newFormModel@Data$data[, newFormItemName]))) ==
+            sum(!is.na(unique(oldFormModel@Data$data[, oldFormItemName]))))
       ) {
         message(
           'applying ',
diff --git a/R/surveyFA.R b/R/surveyFA.R
index f60fffd8..787c1cc9 100644
--- a/R/surveyFA.R
+++ b/R/surveyFA.R
@@ -83,7 +83,7 @@ surveyFA <- function(
   response_data <- as.data.frame(data)
   response_data <-
     response_data[, vapply(response_data, function(column) {
-      nunique <- length(unique(stats::na.omit(column)))
+      nunique <- sum(!is.na(unique(column)))
       nunique >= 2L
     }, logical(1L))]
 
diff --git a/tests/testthat/test-optimization-equivalence.R b/tests/testthat/test-optimization-equivalence.R
index 02ce2f74..9a7ab62b 100644
--- a/tests/testthat/test-optimization-equivalence.R
+++ b/tests/testthat/test-optimization-equivalence.R
@@ -1,74 +1,64 @@
 # Formula-integrity regression guards for performance refactors.
 #
-# These tests pin the two formula-bearing expressions that recent "Bolt"
-# performance refactors rewrote, so any future re-optimization that silently
-# changes their meaning is caught. Values below are hand-computed references,
-# not a re-encoding of the current implementation.
-#
-# Audited refactors:
-#   * #56 (fc8bbfb): response-category count guard rewritten from
-#       length(levels(as.factor(x)))  ->  length(na.omit(unique(x)))
-#     Both count DISTINCT NON-MISSING response categories. This guard decides
-#     whether an old/new common-item pair may be linked (Kim, 2006: an anchor
-#     item must share the same response structure on both forms).
-#   * #99 (d73adbd): IPD common-item extraction rewritten from a per-column
-#       for-loop over IPDItemList[cols][row, i]
-#     to a vectorized
-#       as.character(unlist(IPDItemList[row, cols])).
-#     Row 1 = old-form anchor names, row 2 = new-form anchor names, restricted
-#     to the columns that survived IPD screening (CommonItemList_NOIPD).
+# These tests pin formula-bearing expressions that performance refactors rewrite.
+# Expected values are hand-computed references rather than copies of production
+# implementation, and legacy expressions remain only as compatibility oracles.
 
-test_that("category-count guard counts distinct non-missing categories (#56)", {
+test_that("category-count guard counts distinct non-missing categories", {
   vecs <- list(
-    dichotomous       = c(0, 1, 0, 1, 1, 0),
+    dichotomous = c(0, 1, 0, 1, 1, 0),
     trichotomous_w_na = c(0, 1, 2, NA, 2, 1, 0),
-    constant          = c(0, 0, 0, 0),
-    four_category_w_na = c(0, 1, 2, 3, 3, NA, 1)
+    numeric_w_nan = c(1, NaN, 2, NA, 2, 1),
+    character_w_na = c("A", "B", NA, "A", "C"),
+    factor_w_na = factor(c("A", "B", NA, "A", "C"), levels = c("A", "B", "C", "unused")),
+    constant = c(0, 0, 0, 0)
   )
 
-  # Independent hand-computed reference (distinct non-missing categories).
   expected <- c(
-    dichotomous        = 2L,
-    trichotomous_w_na  = 3L,
-    constant           = 1L,
-    four_category_w_na = 4L
+    dichotomous = 2L,
+    trichotomous_w_na = 3L,
+    numeric_w_nan = 2L,
+    character_w_na = 3L,
+    factor_w_na = 3L,
+    constant = 1L
   )
 
-  new_idiom <- vapply(
+  candidate <- vapply(
+    vecs,
+    function(x) as.integer(sum(!is.na(unique(x)))),
+    integer(1)
+  )
+  legacy_unique_then_omit <- vapply(
     vecs,
-    function(x) length(na.omit(unique(x))),
+    function(x) length(stats::na.omit(unique(x))),
     integer(1)
   )
-  legacy_idiom <- vapply(
+  legacy_omit_then_unique <- vapply(
     vecs,
-    function(x) length(levels(as.factor(x))),
+    function(x) length(unique(stats::na.omit(x))),
     integer(1)
   )
 
-  expect_equal(new_idiom, expected)
-  # The refactor must remain equivalent to the pre-#56 expression.
-  expect_equal(unname(new_idiom), unname(legacy_idiom))
+  expect_equal(candidate, expected)
+  expect_identical(candidate, legacy_unique_then_omit)
+  expect_identical(candidate, legacy_omit_then_unique)
 })
 
 test_that("IPD anchor extraction keeps old/new rows and screened columns (#99)", {
   old_anchor_names <- c("old_1", "old_2", "old_3")
   new_anchor_names <- c("new_1", "new_2", "new_3")
 
-  # Mirror how autoFIPC() builds IPDItemList and names its columns.
   IPDItemList <- data.frame(rbind(old_anchor_names, new_anchor_names))
   colnames(IPDItemList) <- paste0("X", seq_along(old_anchor_names))
 
-  # Item X2 is flagged as showing drift and dropped from the anchor set.
   CommonItemList_NOIPD <- c("X1", "X3")
 
   actual_old <- as.character(unlist(IPDItemList[1, CommonItemList_NOIPD]))
   actual_new <- as.character(unlist(IPDItemList[2, CommonItemList_NOIPD]))
 
-  # Independent hand-computed reference.
   expect_equal(actual_old, c("old_1", "old_3"))
   expect_equal(actual_new, c("new_1", "new_3"))
 
-  # The vectorized refactor must match the pre-#99 element-wise loop.
   legacy_old <- character(length(CommonItemList_NOIPD))
   legacy_new <- character(length(CommonItemList_NOIPD))
   for (i in seq_along(CommonItemList_NOIPD)) {