Add notes about acces log data

app/views/doorkeeper_applications/access_logs.html.erb

@@ -46,6 +46,28 @@
 </div>
 </form>
 
+<%= render "govuk_publishing_components/components/details", {
+  title: "About this data"
+} do %>
+<p class="govuk-body">
+  Signon records a "successful authorization" event whenever a user uses Signon to access one of the publishing
+  applications. This is a record of all of these events for <%= @application.name %>.
+</p>
+<p class="govuk-body">
+  Applications cache authentications for around 20 hours, so if a user clicks an application multiple
+  times a day, they may only appear in the event log once.
+</p>
+<p class="govuk-body">
+  <% if DateTime.current.before? DateTime.new(2025, 11, 1)  # This branch can be removed after November 2025 %>
+  Note that authorization data has only been recorded in the Signon event log since November 2023, so it is not
+  possible to view events before that date.
+  <% else %>
+  Note that data in the event log in Signon is only retained for 2 years, so it is not possible to view events
+  before that date.
+  <% end %>
+</p>
+<% end %>
+
 <% if @logs.any? %>
   <%= render "components/table", {
     caption: pluralize(number_with_delimiter(@logs.total_count), "event"),

app/views/doorkeeper_applications/monthly_access_stats.html.erb

@@ -37,6 +37,35 @@
   } %>
 </form>
 
+<%= render "govuk_publishing_components/components/details", {
+  title: "About this data"
+} do %>
+<p class="govuk-body">
+  Signon records a "successful authorization" event whenever a user uses Signon to access one of the publishing
+  applications. This is a monthly count of all of these events for <%= @application.name %>.
+</p>
+<p class="govuk-body">
+  Applications cache authentications for around 20 hours, so if a user clicks an application multiple
+  times a day, they may only appear in the event log once.
+</p>
+<p class="govuk-body">
+  The total authorization count is the total number of events recorded in the log for the month (if a
+  user accesses the same app multiple times, this number will increase).
+</p>
+<p class="govuk-body">
+  The unique users authorization count is the number of distinct users who recorded events in the log for the month
+  (if a user accesses the same app multiple times in a month, this will only count as one unique user).
+</p>
+<p class="govuk-body">
+  <% if DateTime.current.before? DateTime.new(2025, 11, 1)  # This branch can be removed after November 2025 %>
+  Note that authorization data has only been recorded in the Signon event log since November 2023, so it is not
+  possible to view events before that date.
+  <% else %>
+  Note that data in the event log in Signon is only retained for 2 years, so it is not possible to view events
+  before that date.
+  <% end %>
+</p>
+<% end %>
 <% if @monthly_access_stats.any? %>
   <%= render "components/table", {
     head: [