diff --git a/northd/northd.c b/northd/northd.c
index 01fb59d35e..6c41f52cc8 100644
--- a/northd/northd.c
+++ b/northd/northd.c
@@ -6780,7 +6780,8 @@ build_acl_sample_generic_est_flows(const struct ovn_datapath *od,
     ds_clear(match);
     ds_clear(actions);
 
-    ds_put_cstr(match, "ip && ct.trk && (ct.est || ct.rel) && ");
+    ds_put_cstr(match, "ip && ct.trk && (ct.est || ct.rel) && "
+                       "ct_label.obs_unused == 0 && ");
 
     size_t match_len = match->length;
     ds_put_format(match, "!ct.rpl && ct_mark.obs_collector_id == %"PRIu8" && "
diff --git a/tests/ovn-northd.at b/tests/ovn-northd.at
index b1d8219196..c8a16d1892 100644
--- a/tests/ovn-northd.at
+++ b/tests/ovn-northd.at
@@ -12843,9 +12843,9 @@ AT_CHECK([ovn-sbctl lflow-list | grep -e ls_in_acl_sample -e ls_in_acl_eval -e l
   table=??(ls_in_acl_eval     ), priority=1001 , match=(reg0[[8]] == 1 && (1)), action=(reg8[[16]] = 1; reg0[[13]] = 1; reg3 = 4301; reg9 = 4302; reg8[[0..7]] = 1; reg2[[16..23]] = 1; reg8[[19]] = 0; next;)
   table=??(ls_in_acl_sample   ), priority=0    , match=(1), action=(next;)
   table=??(ls_in_acl_sample   ), priority=1000 , match=(ip && ct.new && reg8[[0..7]] == 1 && reg8[[19]] == 0), action=(sample(probability=65535,collector_set=??,obs_domain=42,obs_point=reg3); next;)
-  table=??(ls_in_acl_sample   ), priority=1000 , match=(ip && ct.trk && (ct.est || ct.rel) && !ct.rpl && ct_mark.obs_collector_id == 1 && ct_mark.obs_after_lb == 0), action=(sample(probability=65535,collector_set=??,obs_domain=43,obs_point=ct_label.obs_point_id); next;)
+  table=??(ls_in_acl_sample   ), priority=1000 , match=(ip && ct.trk && (ct.est || ct.rel) && ct_label.obs_unused == 0 && !ct.rpl && ct_mark.obs_collector_id == 1 && ct_mark.obs_after_lb == 0), action=(sample(probability=65535,collector_set=??,obs_domain=43,obs_point=ct_label.obs_point_id); next;)
   table=??(ls_out_acl_sample  ), priority=0    , match=(1), action=(next;)
-  table=??(ls_out_acl_sample  ), priority=1000 , match=(ip && ct.trk && (ct.est || ct.rel) && ct.rpl && ct_mark.obs_collector_id == 1), action=(sample(probability=65535,collector_set=??,obs_domain=43,obs_point=ct_label.obs_point_id); next;)
+  table=??(ls_out_acl_sample  ), priority=1000 , match=(ip && ct.trk && (ct.est || ct.rel) && ct_label.obs_unused == 0 && ct.rpl && ct_mark.obs_collector_id == 1), action=(sample(probability=65535,collector_set=??,obs_domain=43,obs_point=ct_label.obs_point_id); next;)
 ])
 
 dnl Trace new connections.
@@ -12901,9 +12901,9 @@ AT_CHECK([ovn-sbctl lflow-list | grep -e ls_in_acl_after_lb_sample -e ls_in_acl_
   table=??(ls_in_acl_after_lb_eval), priority=1001 , match=(reg0[[8]] == 1 && (1)), action=(reg8[[16]] = 1; reg0[[13]] = 1; reg3 = 4301; reg9 = 4302; reg8[[0..7]] = 1; reg2[[16..23]] = 1; reg8[[19]] = 1; next;)
   table=??(ls_in_acl_after_lb_sample), priority=0    , match=(1), action=(next;)
   table=??(ls_in_acl_after_lb_sample), priority=1000 , match=(ip && ct.new && reg8[[0..7]] == 1 && reg8[[19]] == 1), action=(sample(probability=65535,collector_set=??,obs_domain=42,obs_point=reg3); next;)
-  table=??(ls_in_acl_after_lb_sample), priority=1000 , match=(ip && ct.trk && (ct.est || ct.rel) && !ct.rpl && ct_mark.obs_collector_id == 1 && ct_mark.obs_after_lb == 1), action=(sample(probability=65535,collector_set=??,obs_domain=43,obs_point=ct_label.obs_point_id); next;)
+  table=??(ls_in_acl_after_lb_sample), priority=1000 , match=(ip && ct.trk && (ct.est || ct.rel) && ct_label.obs_unused == 0 && !ct.rpl && ct_mark.obs_collector_id == 1 && ct_mark.obs_after_lb == 1), action=(sample(probability=65535,collector_set=??,obs_domain=43,obs_point=ct_label.obs_point_id); next;)
   table=??(ls_out_acl_sample  ), priority=0    , match=(1), action=(next;)
-  table=??(ls_out_acl_sample  ), priority=1000 , match=(ip && ct.trk && (ct.est || ct.rel) && ct.rpl && ct_mark.obs_collector_id == 1), action=(sample(probability=65535,collector_set=??,obs_domain=43,obs_point=ct_label.obs_point_id); next;)
+  table=??(ls_out_acl_sample  ), priority=1000 , match=(ip && ct.trk && (ct.est || ct.rel) && ct_label.obs_unused == 0 && ct.rpl && ct_mark.obs_collector_id == 1), action=(sample(probability=65535,collector_set=??,obs_domain=43,obs_point=ct_label.obs_point_id); next;)
 ])
 
 dnl Trace new connections.
@@ -12956,12 +12956,12 @@ check ovn-nbctl acl-del ls
 check ovn-nbctl --wait=sb --sample-new=$sample1 --sample-est=$sample2 acl-add ls to-lport 1 "1" allow-related
 AT_CHECK([ovn-sbctl lflow-list | grep -e ls_out_acl_sample -e ls_out_acl_eval -e ls_in_acl_sample | ovn_strip_lflows | ovn_strip_collector_set | grep -e reg3 -e reg9 -e sample], [0], [dnl
   table=??(ls_in_acl_sample   ), priority=0    , match=(1), action=(next;)
-  table=??(ls_in_acl_sample   ), priority=1000 , match=(ip && ct.trk && (ct.est || ct.rel) && ct.rpl && ct_mark.obs_collector_id == 1), action=(sample(probability=65535,collector_set=??,obs_domain=43,obs_point=ct_label.obs_point_id); next;)
+  table=??(ls_in_acl_sample   ), priority=1000 , match=(ip && ct.trk && (ct.est || ct.rel) && ct_label.obs_unused == 0 && ct.rpl && ct_mark.obs_collector_id == 1), action=(sample(probability=65535,collector_set=??,obs_domain=43,obs_point=ct_label.obs_point_id); next;)
   table=??(ls_out_acl_eval    ), priority=1001 , match=(reg0[[7]] == 1 && (1)), action=(reg8[[16]] = 1; reg0[[1]] = 1; reg0[[13]] = 1; reg3 = 4301; reg9 = 4302; reg8[[0..7]] = 1; reg2[[16..23]] = 1; reg8[[19]] = 0; next;)
   table=??(ls_out_acl_eval    ), priority=1001 , match=(reg0[[8]] == 1 && (1)), action=(reg8[[16]] = 1; reg0[[13]] = 1; reg3 = 4301; reg9 = 4302; reg8[[0..7]] = 1; reg2[[16..23]] = 1; reg8[[19]] = 0; next;)
   table=??(ls_out_acl_sample  ), priority=0    , match=(1), action=(next;)
   table=??(ls_out_acl_sample  ), priority=1000 , match=(ip && ct.new && reg8[[0..7]] == 1 && reg8[[19]] == 0), action=(sample(probability=65535,collector_set=??,obs_domain=42,obs_point=reg3); next;)
-  table=??(ls_out_acl_sample  ), priority=1000 , match=(ip && ct.trk && (ct.est || ct.rel) && !ct.rpl && ct_mark.obs_collector_id == 1 && ct_mark.obs_after_lb == 0), action=(sample(probability=65535,collector_set=??,obs_domain=43,obs_point=ct_label.obs_point_id); next;)
+  table=??(ls_out_acl_sample  ), priority=1000 , match=(ip && ct.trk && (ct.est || ct.rel) && ct_label.obs_unused == 0 && !ct.rpl && ct_mark.obs_collector_id == 1 && ct_mark.obs_after_lb == 0), action=(sample(probability=65535,collector_set=??,obs_domain=43,obs_point=ct_label.obs_point_id); next;)
 ])
 
 dnl Trace new connections.