Provide guidance on choosing validity periods for status lists.

index.html

@@ -1678,6 +1678,46 @@ <h3>Bitstring Encoding</h3>
       </p>
     </section>
 
+    <section class="informative">
+      <h3>Validity Periods</h3>
+
+      <p>
+The <a data-cite="?VC-DATA-MODEL-2.0#validity-period">validity period</a> that
+an issuer might choose to express in a status list is dependent on a variety of
+factors including:
+      </p>
+      <ul>
+        <li>
+How often do status values change? In real-time? Daily? Weekly? Monthly? Other?
+        </li>
+        <li>
+Is there a regulatory requirement that compels an [=issuer=] to notify a
+[=verifier=] that the status of a [=verifiable credential=] has changed?
+        </li>
+        <li>
+Is there a period of time after which an [=issuer=] would incur reputational
+damage by not notifying a [=verifier=] of a status change?
+        </li>
+        <li>
+Is there any expectation that a [=verifier=] will not accept a
+[=verifiable credential=] with a status list that does not expire for a
+period of time it deems excessive?
+        </li>
+        <li>
+Will a short validity period for a status list cause a significant network
+bandwidth or computing burden for an [=issuer=] or a [=verifier=]? Might
+this burden be mitigated by a longer validity period?
+        </li>
+      </ul>
+
+      <p>
+Since these factors vary with the ecosystem and credential type, there is no
+minimum or maximum validity period that is suggested for all status lists.
+[=Issuers=] will need to consider various factors that are specific to their
+[=verifiable credential=] types and choose validity periods that will strike
+the right balance in their ecosystem.
+      </p>
+    </section>
 
   </section>