chunks 1-4: Repair the .AT and .UC macros (committed upstream, too).
chunk 2: Tweak section headers (local change).
chunk 3: Set the default operating system name (local change).

Index: tmac/an-old.tmac
--- tmac/an-old.tmac.orig
+++ tmac/an-old.tmac
@@ -146,29 +146,6 @@
 .    DEVTAG-EO-TL
 .  \}
 .
-.  de an-init \" This approach gets multiple man pages right.
-.    ds an-title "\\$1\"
-.    ds an-section "\\$2\"
-.    ds an-extra1 "\\$3\"
-.    ie (\\n[.$] > 3)    .ds an-extra2 "\\$4\"
-.    el                  .ds an-extra2 \"Sun Release 4.0
-.
-.    ie (\\n[.$] > 4)    .ds an-extra3 "\\$5\"
-.    el \{ .ie '\\$2'1'  .ds an-extra3 General Commands Manual
-.    el \{ .ie '\\$2'2'  .ds an-extra3 System Calls Manual
-.    el \{ .ie '\\$2'3'  .ds an-extra3 Library Functions Manual
-.    el \{ .ie '\\$2'3p' .ds an-extra3 Perl Programmers Reference Guide
-.    el \{ .ie '\\$2'4'  .ds an-extra3 Kernel Interfaces Manual
-.    el \{ .ie '\\$2'5'  .ds an-extra3 File Formats Manual
-.    el \{ .ie '\\$2'6'  .ds an-extra3 Games Manual
-.    el \{ .ie '\\$2'7'  .ds an-extra3 Miscellaneous Information Manual
-.    el \{ .ie '\\$2'8'  .ds an-extra3 System Manager's Manual
-.    el \{ .ie '\\$2'9'  .ds an-extra3 Kernel Developer's Manual
-.    el                  .ds an-extra3
-.    \}\}\}\}\}\}\}\}\}\}
-.    ds an-init
-\\..
-.
 .  DT
 .
 .  nr PS    10z \" default point size
@@ -214,6 +191,22 @@
 .  nr an-break-flag 0
 .  nr an-div? 0
 .
+.  ds an-title "\\$1\"
+.  ds an-section "\\$2\"
+.    ie (\\n[.$] > 4)    .ds an-extra3 "\\$5\"
+.    el \{ .ie '\\$2'1'  .ds an-extra3 General Commands Manual
+.    el \{ .ie '\\$2'2'  .ds an-extra3 System Calls Manual
+.    el \{ .ie '\\$2'3'  .ds an-extra3 Library Functions Manual
+.    el \{ .ie '\\$2'3p' .ds an-extra3 Perl Library Manual
+.    el \{ .ie '\\$2'4'  .ds an-extra3 Device Drivers Manual
+.    el \{ .ie '\\$2'5'  .ds an-extra3 File Formats Manual
+.    el \{ .ie '\\$2'6'  .ds an-extra3 Games Manual
+.    el \{ .ie '\\$2'7'  .ds an-extra3 Miscellaneous Information Manual
+.    el \{ .ie '\\$2'8'  .ds an-extra3 System Manager's Manual
+.    el \{ .ie '\\$2'9'  .ds an-extra3 Kernel Developer's Manual
+.    el                  .ds an-extra3
+.    \}\}\}\}\}\}\}\}\}\}
+.
 .  ie \\n[cR] \
 .    an-header
 .  el \{\
@@ -226,6 +219,10 @@
 .      el        .bp 1
 .    \}
 .  \}
+.
+.  ds an-extra1 "\\$3\"
+.  ie (\\n[.$] > 3)    .ds an-extra2 "\\$4\"
+.  el                  .ds an-extra2 OpenBSD
 ..
 .
 .\" BSD compatibility macros: .AT and .UC
@@ -276,7 +273,6 @@
 ..
 .
 .de1 an-header
-.  an-init
 .  if \\n[cR] \{\
 .    ie \\n[an-first] \
 .      nr an-first 0