Attempting to pull a static tag by date is A Bad Thing(tm). Just don't do it (because cvs won't).

client.mk

@@ -210,11 +210,15 @@ NSS_CO_MODULE = mozilla/security/nss \
 ifdef MOZ_NSS_AUTOCONF
 NSS_CO_TAG = NSS_CLIENT_BRANCH
 endif
-		
+
 NSS_CO_FLAGS := -P
 ifdef NSS_CO_TAG
    NSS_CO_FLAGS := $(NSS_CO_FLAGS) -r $(NSS_CO_TAG)
 endif
+# Cannot pull static tags by date
+ifeq ($(NSS_CO_TAG),NSS_CLIENT_TAG)
+CVS_CO_DATE_FLAGS :=
+endif
 CVSCO_NSS = $(CVS) $(CVS_FLAGS) co $(NSS_CO_FLAGS) $(CVS_CO_DATE_FLAGS) $(NSS_CO_MODULE)
 
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