diff --git a/admin/app/services/map_service.ts b/admin/app/services/map_service.ts
index 0e1c902..9de8c49 100644
--- a/admin/app/services/map_service.ts
+++ b/admin/app/services/map_service.ts
@@ -457,6 +457,18 @@ export class MapService implements IMapService {
     return await listDirectoryContentsRecursive(this.baseDirPath)
   }
 
+  /**
+   * Compare two map-file versions (YYYY-MM, or null for an undated legacy file). Returns >0 if
+   * `a` is newer than `b`, <0 if older, 0 if equal. A dated build is always newer than an undated
+   * legacy file; two dated builds compare lexicographically (correct for zero-padded YYYY-MM).
+   */
+  private static compareMapVersions(a: string | null, b: string | null): number {
+    if (a === b) return 0
+    if (a === null) return -1
+    if (b === null) return 1
+    return a < b ? -1 : 1
+  }
+
   private generateSourcesArray(host: string | null, regions: FileEntry[], protocol: string = 'http'): BaseStylesFile['sources'][] {
     const sources: BaseStylesFile['sources'][] = []
     const baseUrl = this.getPublicFileBaseUrl(host, 'pmtiles', protocol)
@@ -474,23 +486,47 @@ export class MapService implements IMapService {
       sources.push(worldSource)
     }
 
+    // Dedupe by region name, keeping only the newest file per region. The source name is the
+    // date-stripped region (e.g. both "washington.pmtiles" and "washington_2025-12.pmtiles" map
+    // to "washington"). Emitting both produces duplicate source keys and duplicate layer ids,
+    // which MapLibre rejects outright — blanking the ENTIRE map, not just that region. Old copies
+    // linger when a newer curated version installs (#634), so guard against it here so the style
+    // stays valid even if cleanup hasn't run. A dated build beats an undated legacy file; between
+    // two dated builds the later YYYY-MM wins (lexicographic compare is correct for that format).
+    const bestByRegion = new Map<string, { region: FileEntry; version: string | null }>()
     for (const region of regions) {
       if (region.type === 'file' && region.name.endsWith('.pmtiles')) {
-        // Strip .pmtiles and date suffix (e.g. "alaska_2025-12" -> "alaska") for stable source names
         const parsed = CollectionManifestService.parseMapFilename(region.name)
         const regionName = parsed ? parsed.resource_id : region.name.replace('.pmtiles', '')
-        const source: BaseStylesFile['sources'] = {}
-        const sourceUrl = urlJoin(baseUrl, region.name)
-
-        source[regionName] = {
-          type: 'vector',
-          attribution: PMTILES_ATTRIBUTION,
-          url: `pmtiles://${sourceUrl}`,
+        const version = parsed?.version ?? null
+        const existing = bestByRegion.get(regionName)
+        if (!existing || MapService.compareMapVersions(version, existing.version) > 0) {
+          if (existing) {
+            logger.warn(
+              `[MapService] Duplicate map region "${regionName}": using "${region.name}" over "${existing.region.name}" (keeping newest)`
+            )
+          }
+          bestByRegion.set(regionName, { region, version })
+        } else {
+          logger.warn(
+            `[MapService] Duplicate map region "${regionName}": skipping "${region.name}" in favor of "${existing.region.name}" (keeping newest)`
+          )
         }
-        sources.push(source)
       }
     }
 
+    for (const [regionName, { region }] of bestByRegion) {
+      const source: BaseStylesFile['sources'] = {}
+      const sourceUrl = urlJoin(baseUrl, region.name)
+
+      source[regionName] = {
+        type: 'vector',
+        attribution: PMTILES_ATTRIBUTION,
+        url: `pmtiles://${sourceUrl}`,
+      }
+      sources.push(source)
+    }
+
     return sources
   }