diff --git a/tpl/templates/templates_integration_test.go b/tpl/templates/templates_integration_test.go
index 4150ec367..93922b4c4 100644
--- a/tpl/templates/templates_integration_test.go
+++ b/tpl/templates/templates_integration_test.go
@@ -214,3 +214,18 @@ All.
 	b.AssertFileContent("public/index.html", "All.")
 	b.AssertFileContent("public/amp/index.html", "All.")
 }
+
+// Issue #13584.
+func TestLegacySectionSection(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- hugo.toml --
+-- content/mysection/_index.md --
+-- layouts/section/section.html --
+layouts/section/section.html
+
+`
+	b := hugolib.Test(t, files)
+	b.AssertFileContent("public/mysection/index.html", "layouts/section/section.html")
+}
diff --git a/tpl/tplimpl/templates.go b/tpl/tplimpl/templates.go
index 1f911b9a5..4c3ad3be1 100644
--- a/tpl/tplimpl/templates.go
+++ b/tpl/tplimpl/templates.go
@@ -3,7 +3,9 @@ package tplimpl
 import (
 	"io"
 	"regexp"
+	"strconv"
 	"strings"
+	"sync/atomic"
 	"unicode"
 	"unicode/utf8"
 
@@ -49,11 +51,6 @@ func (t *templateNamespace) parseTemplate(ti *TemplInfo) error {
 	}
 	pi := ti.PathInfo
 	name := pi.PathNoLeadingSlash()
-	if ti.isLegacyMapped {
-		// When mapping the old taxonomy structure to the new one, we may map the same path to multiple templates per kind.
-		// Append the kind here to make the name unique.
-		name += ("-" + ti.D.Kind)
-	}
 
 	var (
 		templ tpl.Template
@@ -62,12 +59,18 @@ func (t *templateNamespace) parseTemplate(ti *TemplInfo) error {
 
 	if ti.D.IsPlainText {
 		prototype := t.parseText
+		if prototype.Lookup(name) != nil {
+			name += "-" + strconv.FormatUint(t.nameCounter.Add(1), 10)
+		}
 		templ, err = prototype.New(name).Parse(ti.content)
 		if err != nil {
 			return err
 		}
 	} else {
 		prototype := t.parseHTML
+		if prototype.Lookup(name) != nil {
+			name += "-" + strconv.FormatUint(t.nameCounter.Add(1), 10)
+		}
 		templ, err = prototype.New(name).Parse(ti.content)
 		if err != nil {
 			return err
@@ -296,6 +299,8 @@ type templateNamespace struct {
 	prototypeText *texttemplate.Template
 	prototypeHTML *htmltemplate.Template
 
+	nameCounter atomic.Uint64
+
 	standaloneText *texttemplate.Template
 
 	baseofTextClones []*texttemplate.Template
diff --git a/tpl/tplimpl/templatestore.go b/tpl/tplimpl/templatestore.go
index 3c8c4abf2..8fe89586d 100644
--- a/tpl/tplimpl/templatestore.go
+++ b/tpl/tplimpl/templatestore.go
@@ -690,7 +690,7 @@ func (t *TemplateStore) UnusedTemplates() []*TemplInfo {
 	var unused []*TemplInfo
 
 	for vv := range t.templates() {
-		if vv.subCategory != SubCategoryMain {
+		if vv.subCategory != SubCategoryMain || vv.isLegacyMapped {
 			// Skip inline partials and internal templates.
 			continue
 		}
@@ -1169,8 +1169,8 @@ func (s *TemplateStore) insertTemplates(include func(fi hugofs.FileMetaInfo) boo
 		case containerPartials, containerShortcodes, containerMarkup:
 			// OK.
 		default:
-			applyLegacyMapping = true
 			pi = fromLegacyPath(pi)
+			applyLegacyMapping = strings.Count(pi.Path(), "/") <= 2
 		}
 
 		if applyLegacyMapping {
@@ -1183,6 +1183,7 @@ func (s *TemplateStore) insertTemplates(include func(fi hugofs.FileMetaInfo) boo
 					ext:            pi.Ext(),
 					outputFormat:   pi.OutputFormat(),
 				}
+
 				if m2, ok := legacyOrdinalMappings[key]; ok {
 					if m1.ordinal < m2.m.ordinal {
 						// Higher up == better match.
@@ -1208,26 +1209,74 @@ func (s *TemplateStore) insertTemplates(include func(fi hugofs.FileMetaInfo) boo
 
 			base := piOrig.PathBeforeLangAndOutputFormatAndExt()
 			identifiers := pi.IdentifiersUnknown()
-
-			// Tokens on e.g. form /SECTIONKIND/THESECTION
-			insertSectionTokens := func(section string, kindOnly bool) string {
-				s := base
-				if !kindOnly {
-					s = strings.Replace(s, section, sectionToken, 1)
-				}
-				s = strings.Replace(s, kinds.KindSection, sectionKindToken, 1)
-				return s
+			if pi.Kind() != "" {
+				identifiers = append(identifiers, pi.Kind())
 			}
 
-			for _, section := range identifiers {
-				if section == baseNameBaseof {
+			shouldIncludeSection := func(section string) bool {
+				switch section {
+				case containerShortcodes, containerPartials, containerMarkup:
+					return false
+				case "taxonomy", "":
+					return false
+				default:
+					for k, v := range s.opts.TaxonomySingularPlural {
+						if k == section || v == section {
+							return false
+						}
+					}
+					return true
+				}
+			}
+			if shouldIncludeSection(pi.Section()) {
+				identifiers = append(identifiers, pi.Section())
+			}
+
+			identifiers = helpers.UniqueStrings(identifiers)
+
+			// Tokens on e.g. form /SECTIONKIND/THESECTION
+			insertSectionTokens := func(section string) []string {
+				kindOnly := isLayoutStandard(section)
+				var ss []string
+				s1 := base
+				if !kindOnly {
+					s1 = strings.ReplaceAll(s1, section, sectionToken)
+				}
+				s1 = strings.ReplaceAll(s1, kinds.KindSection, sectionKindToken)
+				if s1 != base {
+					ss = append(ss, s1)
+				}
+				s1 = strings.ReplaceAll(base, kinds.KindSection, sectionKindToken)
+				if !kindOnly {
+					s1 = strings.ReplaceAll(s1, section, sectionToken)
+				}
+				if s1 != base {
+					ss = append(ss, s1)
+				}
+
+				helpers.UniqueStringsReuse(ss)
+
+				return ss
+			}
+
+			for _, id := range identifiers {
+				if id == "" {
 					continue
 				}
-				kindOnly := isLayoutStandard(section)
-				p := insertSectionTokens(section, kindOnly)
-				if m1, ok := s.opts.legacyMappingSection[p]; ok {
-					m1.mapping.targetPath = strings.Replace(m1.mapping.targetPath, sectionToken, section, 1)
-					handleMapping(m1)
+
+				p := insertSectionTokens(id)
+				for _, ss := range p {
+					if m1, ok := s.opts.legacyMappingSection[ss]; ok {
+						targetPath := m1.mapping.targetPath
+
+						if targetPath != "" {
+							targetPath = strings.ReplaceAll(targetPath, sectionToken, id)
+							targetPath = strings.ReplaceAll(targetPath, sectionKindToken, id)
+							targetPath = strings.ReplaceAll(targetPath, "//", "/")
+						}
+						m1.mapping.targetPath = targetPath
+						handleMapping(m1)
+					}
 				}
 			}
 
diff --git a/tpl/tplimpl/templatestore_integration_test.go b/tpl/tplimpl/templatestore_integration_test.go
index 4f76626ad..74abe58d0 100644
--- a/tpl/tplimpl/templatestore_integration_test.go
+++ b/tpl/tplimpl/templatestore_integration_test.go
@@ -441,7 +441,7 @@ title: "P1"
 {{ define "main" }}FOO{{ end }}
 -- layouts/_default/single.json --
 -- layouts/_default/single.html --
-{{ define "main" }}MAIN{{ end }}
+{{ define "main" }}MAIN /_default/single.html{{ end }}
 -- layouts/post/single.html --
 {{ define "main" }}MAIN{{ end }}
 -- layouts/_partials/usedpartial.html --
@@ -461,6 +461,8 @@ title: "P1"
 	)
 	b.Build()
 
+	b.AssertFileContent("public/p1/index.html", "MAIN /_default/single.html")
+
 	unused := b.H.GetTemplateStore().UnusedTemplates()
 	var names []string
 	for _, tmpl := range unused {
@@ -468,8 +470,9 @@ title: "P1"
 			names = append(names, fi.Meta().PathInfo.PathNoLeadingSlash())
 		}
 	}
-	b.Assert(len(unused), qt.Equals, 5, qt.Commentf("%#v", names))
+
 	b.Assert(names, qt.DeepEquals, []string{"_partials/unusedpartial.html", "shortcodes/unusedshortcode.html", "baseof.json", "post/single.html", "_default/single.json"})
+	b.Assert(len(unused), qt.Equals, 5, qt.Commentf("%#v", names))
 }
 
 func TestCreateManyTemplateStores(t *testing.T) {