I did this according to the Aperture 3 Manual:
"...select an image and choose Photos > Edit With > [application name]. Aperture makes a new master and version of your image and opens it in Adobe Photoshop. After you make your changes and save the image, the revised version automatically reappears in Aperture. The external editor doesn’t change the original master."
I exported the RAW file as a 16-bit PSD file, made changes and I saved the Photoshop edited file with the same file name. It updated the Aperture image, but there is no other image, just the PS-edited file with the sigil that means "The photo has been edited with an external editor, and is therefore represented by the original created when the file was exported to the external editor."
But I cannot see the original master file. It's not stacked, it's not moved, it's simply gone. How do I get the original RAW master back along side the PS edited version to make more/other edits?
Are your raw files part of a raw+jpeg pair or raw-only?
When I tried to reproduce your problem, but for me the external edit is working as described in the manual.
- Set the "External Editor Format" to 16 bit psd in the "Export" preferences.
- Select the image in Aperture's browser and use the command "Photos > Edit with Adobe Photoshop CS 6"
- Edit Photoshop and use "File > Save", not "Save as".
What exactly do you see, when you are using Photoshop as an external editor?
As soon as I use "Photos > Edit with Adobe Photoshop CS 6", the new PSD version will appear alongside the raw, and after I save the file in Photoshop, the thumbnail will be updated.
Do you also see the new version appear, before Photoshop opens?
The only way I cannot see the versions side by side, is if I do not set the sorting in the browser to "Date", or if the search field is not cleared. You may want to check the sorting of the project and check for filters.
For example: Editing a raw-jpeg pair, first with "8bit tiff" export, then with "16bit psd" export.
If clearing filters and changing the sorting does not bring the original back, I'd try to repair the Aperture library - this may recover missing originals in a "Recovered" project.