spec: elaborate on how optional this is
diff --git a/docs/imsi-pseudo-spec.adoc b/docs/imsi-pseudo-spec.adoc
index 82270fd..0d2cccb 100644
--- a/docs/imsi-pseudo-spec.adoc
+++ b/docs/imsi-pseudo-spec.adoc
@@ -192,7 +192,9 @@
=== Process Update_Location_HLR
All IMSI Pseudonymization related changes to Process Update_Location_HLR
-(3GPP TS 29.002) are optional.
+(3GPP TS 29.002) are optional. All deviations from the existing specification
+that are outlined in this section are expected to be enabled or disabled
+entirely where IMSI pseudonymization is implemented.
* HLR looks up subscriber by pseudonymous imsi in Update Location Request
* if two pseudo imsi found, and connected with new one: dealloc old entry