diff --git a/rslib/src/scheduler/fsrs/simulator.rs b/rslib/src/scheduler/fsrs/simulator.rs
index 595f2a028..42810dd49 100644
--- a/rslib/src/scheduler/fsrs/simulator.rs
+++ b/rslib/src/scheduler/fsrs/simulator.rs
@@ -153,6 +153,7 @@ impl Collection {
             .filter_map(|c| {
                 let memory_state = match c.memory_state {
                     Some(state) => state,
+                    // cards that lack memory states after compute_memory_state have no FSRS items, implying a truncated or ignored revlog
                     None => fsrs
                         .memory_state_from_sm2(
                             c.ease_factor(),