Yeah.  The set of files that influence the combined worker are the set of files that are printed out as the dependency list, e.g.:

```
     [exec] Tracing dependencies for: Workers/createVerticesFromHeightmap
     [exec]
     [exec] C:/git/cesium/Build/combineOutput/Workers/createVerticesFromHeightmap.js
     [exec] ----------------
     [exec] C:/git/cesium/Source/Core/freezeObject.js
     [exec] C:/git/cesium/Source/Core/defaultValue.js
     [exec] C:/git/cesium/Source/Core/DeveloperError.js
     [exec] C:/git/cesium/Source/Core/Cartesian2.js
     [exec] C:/git/cesium/Source/Core/Cartesian3.js
     [exec] C:/git/cesium/Source/Core/Cartesian4.js
     [exec] C:/git/cesium/Source/Core/Math.js
     [exec] C:/git/cesium/Source/Core/Cartographic.js
     [exec] C:/git/cesium/Source/Core/Ellipsoid.js
     [exec] C:/git/cesium/Source/Core/GeographicProjection.js
     [exec] C:/git/cesium/Source/Core/Extent.js
     [exec] C:/git/cesium/Source/Core/Enumeration.js
     [exec] C:/git/cesium/Source/Core/Intersect.js
     [exec] C:/git/cesium/Source/Core/Interval.js
     [exec] C:/git/cesium/Source/Core/Matrix3.js
     [exec] C:/git/cesium/Source/Core/RuntimeError.js
     [exec] C:/git/cesium/Source/Core/Matri
     [exec] x4.js
     [exec] C:/git/cesium/Source/Core/BoundingSphere.js
     [exec] C:/git/cesium/Source/Core/getImagePixels.js
     [exec] C:/git/cesium/Source/Core/ComponentDatatype.js
     [exec] C:/git/cesium/Source/Core/PrimitiveType.js
     [exec] C:/git/cesium/Source/Core/HeightmapTessellator.js
     [exec] C:/git/cesium/Source/Core/Visibility.js
     [exec] C:/git/cesium/Source/Core/Occluder.js
     [exec] C:/git/cesium/Source/Workers/createTaskProcessorWorker.js
     [exec] C:/git/cesium/Source/Workers/createVerticesFromHeightmap.js
```

I think that if you store this list of dependencies somewhere, for each worker, you can check the mod times for that list of files the next time you build, and you can trust that if none of those files are newer than the generated file, then the generated file is up to date.