diff --git a/backend/mpc-system/services/session-coordinator/domain/entities/mpc_session.go b/backend/mpc-system/services/session-coordinator/domain/entities/mpc_session.go
index a6976405..69d6d177 100644
--- a/backend/mpc-system/services/session-coordinator/domain/entities/mpc_session.go
+++ b/backend/mpc-system/services/session-coordinator/domain/entities/mpc_session.go
@@ -142,27 +142,27 @@ func (s *MPCSession) UpdateParticipantStatus(partyID value_objects.PartyID, stat
 }
 
 // CanStart checks if all participants have joined and the session can start
-//
-// BREAKING CHANGE WARNING (for co-sign feature, commit 99fa003b):
-// Original code: len(s.Participants) == s.Threshold.N() && readyCount == s.Threshold.N()
-// New code: Check all registered participants are joined (no T/N check)
-// This change affects PERSISTENT SIGN flow because we now pass keygenThresholdN
-// instead of len(parties) as threshold_n. With original code, sign sessions with
-// T+1 participants would fail because T+1 != N.
-// If issues arise with persistent sign, REVERT to original N-based check.
-// Related files: session_coordinator.go, session_coordinator_client.go, account_handler.go
 func (s *MPCSession) CanStart() bool {
-	// Session can start when all registered participants have joined
-	// The number of participants was determined at session creation time:
-	// - For keygen: N parties are registered
-	// - For sign: T or T+1 parties are registered (depending on the signing flow)
-	// We don't need to check against T or N here - just verify all registered parties have joined
+	// For keygen sessions (including co-managed keygen): must have exactly N participants
+	if s.SessionType.IsKeygen() {
+		if len(s.Participants) != s.Threshold.N() {
+			return false
+		}
+		readyCount := 0
+		for _, p := range s.Participants {
+			if p.IsJoined() || p.IsReady() {
+				readyCount++
+			}
+		}
+		return readyCount == s.Threshold.N()
+	}
+
+	// For sign sessions: check all registered participants have joined
+	// The number of participants was determined at session creation time (T or T+1)
 	if len(s.Participants) == 0 {
 		return false
 	}
-
 	for _, p := range s.Participants {
-		// All participants must be in joined or ready status
 		if !p.IsJoined() && !p.IsReady() {
 			return false
 		}
@@ -272,15 +272,21 @@ func (s *MPCSession) MarkPartyReady(partyID string) error {
 }
 
 // AllPartiesReady checks if all participants are ready
-//
-// BREAKING CHANGE WARNING (for co-sign feature, commit 99fa003b):
-// Original code: len(s.Participants) != s.Threshold.N() would return false
-// New code: Check all registered participants are ready (no T/N check)
-// This change affects PERSISTENT SIGN flow. See CanStart() for details.
-// If issues arise with persistent sign, REVERT to original N-based check.
 func (s *MPCSession) AllPartiesReady() bool {
-	// Check that all registered participants are ready or completed
-	// The participant count was determined at session creation time
+	// For keygen sessions: must have exactly N participants
+	if s.SessionType.IsKeygen() {
+		if len(s.Participants) != s.Threshold.N() {
+			return false
+		}
+		for _, p := range s.Participants {
+			if !p.IsReady() && !p.IsCompleted() {
+				return false
+			}
+		}
+		return true
+	}
+
+	// For sign sessions: check all registered participants are ready
 	if len(s.Participants) == 0 {
 		return false
 	}