The macOS probe covered five of the six shapes RFC 6350 section 4.3.1
admits; month alone had no card to serve.

Assisted-by: Claude Opus 5 via Claude Code

diff --git a/test/fixtures/cards/bday-month-only.vcf b/test/fixtures/cards/bday-month-only.vcf
new file mode 100644
index 0000000..f556f94
--- /dev/null
+++ b/test/fixtures/cards/bday-month-only.vcf
@@ -0,0 +1,7 @@
+BEGIN:VCARD
+VERSION:3.0
+N:Birthday;Month Only;;;
+FN:Month Only Birthday
+BDAY:--04
+UID:bday-month-only
+END:VCARD
diff --git a/test/fixtures/macos-exchange/05-propfind-addressbook-ctag/response b/test/fixtures/macos-exchange/05-propfind-addressbook-ctag/response
index 42ef58d..5bf90d7 100644
--- a/test/fixtures/macos-exchange/05-propfind-addressbook-ctag/response
+++ b/test/fixtures/macos-exchange/05-propfind-addressbook-ctag/response
@@ -16,8 +16,8 @@ Content-Type: text/xml
           <d:report><d:sync-collection/></d:report>
         </d:supported-report>
       </d:supported-report-set>
-      <cs:getctag>8d49f12d5a21ce322b92458f141a911457556c0113fa89bbb6d647264744a0d9</cs:getctag>
-      <d:sync-token>http://pro-tacts/sync/8d49f12d5a21ce322b92458f141a911457556c0113fa89bbb6d647264744a0d9</d:sync-token>
+      <cs:getctag>dd8f4d6dc8fa74f0ea9abdc089a0b2a9c1c5a548ee3f2812c3ee7e6abbfbf1cb</cs:getctag>
+      <d:sync-token>http://pro-tacts/sync/dd8f4d6dc8fa74f0ea9abdc089a0b2a9c1c5a548ee3f2812c3ee7e6abbfbf1cb</d:sync-token>
       <d:current-user-privilege-set>
         <d:privilege><d:read/></d:privilege>
         <d:privilege><d:write/></d:privilege>
diff --git a/test/fixtures/macos-exchange/06-propfind-addressbook-listing/response b/test/fixtures/macos-exchange/06-propfind-addressbook-listing/response
index 26e8c89..2c255c8 100644
--- a/test/fixtures/macos-exchange/06-propfind-addressbook-listing/response
+++ b/test/fixtures/macos-exchange/06-propfind-addressbook-listing/response
@@ -67,6 +67,15 @@ Content-Type: text/xml
     <d:status>HTTP/1.1 200 OK</d:status>
   </d:propstat>
 </d:response>
+<d:response>
+  <d:href>/dav/addressbook/bday-month-only.vcf</d:href>
+  <d:propstat>
+    <d:prop>
+      <d:getetag>"9e74786a9f63faee3401fbb02a58da8ee8238d358d9378bc9487c4c3ad3c33a7"</d:getetag>
+    </d:prop>
+    <d:status>HTTP/1.1 200 OK</d:status>
+  </d:propstat>
+</d:response>
 <d:response>
   <d:href>/dav/addressbook/bday-omit-year.vcf</d:href>
   <d:propstat>
diff --git a/test/fixtures/macos-exchange/08-report-sync-collection/response b/test/fixtures/macos-exchange/08-report-sync-collection/response
index 6da3896..89d0203 100644
--- a/test/fixtures/macos-exchange/08-report-sync-collection/response
+++ b/test/fixtures/macos-exchange/08-report-sync-collection/response
@@ -66,6 +66,15 @@ Content-Type: text/xml
     <d:status>HTTP/1.1 200 OK</d:status>
   </d:propstat>
 </d:response>
+<d:response>
+  <d:href>/dav/addressbook/bday-month-only.vcf</d:href>
+  <d:propstat>
+    <d:prop>
+      <d:getetag>"9e74786a9f63faee3401fbb02a58da8ee8238d358d9378bc9487c4c3ad3c33a7"</d:getetag>
+    </d:prop>
+    <d:status>HTTP/1.1 200 OK</d:status>
+  </d:propstat>
+</d:response>
 <d:response>
   <d:href>/dav/addressbook/bday-omit-year.vcf</d:href>
   <d:propstat>
diff --git a/test/fixtures/macos-exchange/09-propfind-addressbook-bootstrap/response b/test/fixtures/macos-exchange/09-propfind-addressbook-bootstrap/response
index 4bae886..b5bea47 100644
--- a/test/fixtures/macos-exchange/09-propfind-addressbook-bootstrap/response
+++ b/test/fixtures/macos-exchange/09-propfind-addressbook-bootstrap/response
@@ -16,8 +16,8 @@ Content-Type: text/xml
           <d:report><d:sync-collection/></d:report>
         </d:supported-report>
       </d:supported-report-set>
-      <cs:getctag>8d49f12d5a21ce322b92458f141a911457556c0113fa89bbb6d647264744a0d9</cs:getctag>
-      <d:sync-token>http://pro-tacts/sync/8d49f12d5a21ce322b92458f141a911457556c0113fa89bbb6d647264744a0d9</d:sync-token>
+      <cs:getctag>dd8f4d6dc8fa74f0ea9abdc089a0b2a9c1c5a548ee3f2812c3ee7e6abbfbf1cb</cs:getctag>
+      <d:sync-token>http://pro-tacts/sync/dd8f4d6dc8fa74f0ea9abdc089a0b2a9c1c5a548ee3f2812c3ee7e6abbfbf1cb</d:sync-token>
       <d:current-user-privilege-set>
         <d:privilege><d:read/></d:privilege>
         <d:privilege><d:write/></d:privilege>
@@ -92,6 +92,15 @@ Content-Type: text/xml
     <d:status>HTTP/1.1 200 OK</d:status>
   </d:propstat>
 </d:response>
+<d:response>
+  <d:href>/dav/addressbook/bday-month-only.vcf</d:href>
+  <d:propstat>
+    <d:prop>
+      <d:getetag>"9e74786a9f63faee3401fbb02a58da8ee8238d358d9378bc9487c4c3ad3c33a7"</d:getetag>
+    </d:prop>
+    <d:status>HTTP/1.1 200 OK</d:status>
+  </d:propstat>
+</d:response>
 <d:response>
   <d:href>/dav/addressbook/bday-omit-year.vcf</d:href>
   <d:propstat>