\ref can take a list of stanza numbers now

basic_format_and_style_settings.ly

@@ -24,6 +24,11 @@
   markup-system-spacing = #'((basic-distance . 1))
   score-markup-spacing = #'((padding . 2))
   top-markup-spacing = #'((basic-distance . 0) (minimum-distance . 0) (padding . 0))
+  refMarkupFormatter = #(lambda (layout props stanzanumbers)
+    (interpret-markup layout props
+    (if (null? stanzanumbers)
+        refString
+        (ly:format refStringWithNumbers (string-join (map (lambda (stanzanumber) (ly:format "~a." stanzanumber)) stanzanumbers) ", ")))))
 }
 
 generalLayout = \layout {
@@ -125,10 +130,15 @@ stanza =
 #}
 )
 
-ref = {
-  \once \override StanzaNumber.layer = 23 % set this to signal that there is a real stanza and no repeat signs
-  \set stanza = \refString
-}
+ref =
+#(define-music-function (stanzanumbers lyrics) ((number-list? (list)) ly:music?)
+#{ \lyricmode {
+    \once \override StanzaNumber.layer = 23 % set this to signal that there is a real stanza and no repeat signs
+    \set stanza = #(make-on-the-fly-markup (lambda (layout props m) ((ly:output-def-lookup layout 'refMarkupFormatter) layout props stanzanumbers)) (make-null-markup))
+    #lyrics
+  }
+#}
+)
 
 % prints a repStart Sign as stanza if the tag 'repeats is kept.
 % if there was a stanza already set by the stanza function with StanzaNumber.layer = 23 we set that also as stanza.

default_style.ly

@@ -18,6 +18,7 @@ lyricSize = 1.6
 stanzaFormat = "~a."
 romanStanzaFormat = "~@r."
 refString = "Ref.:"
+refStringWithNumbers = "Ref. ~a:"
 % hübsche Wiederholungszeichen für den Liedtext
 repStart = "𝄆"
 repStop = "𝄇"