I can't advise the best way forward to fix this, but here is some information.
Option 1:Yes, you can export individual Views in MC Standard View to files and import them into your earlier Library. As long as you haven't created any new fields to use in the Views, they will work straight away. If you have created new fields, you will need to create the new fields in your old Library and then import the Views. The functions are under the "Customise View" right-click menu item, at the bottom of the "Settings" dialogue. The files are saved in "C:\Users\[UserID]\AppData\Roaming\J River\Media Center 25\Library\Saved Views\" for MC25. Theatre View views are a little more difficult if you built them directly, as there is no equivalent functionality. But if you built a View in MC Standard View, then saved that, imported it into another Library, you can base a Theatre View view on that imported View. Or just take screenshots of any Theatre View only Views, and re-create them in the other Library directly.
If you have done a lot of tagging work that you want to save, if the tags are in the files all you need to do it run the function "Library Tools > Update Library (from tags)" for all the affected files. Of course not all tags are saved into media files or the MC Sidecar files. But you can turn on saving of any tags via the "Options > Library & Folders > Manage Library Fields > {select the tag you want to be saved} > Save in file tags (when possible)" checkbox. For Video and some other files types, that means turning on the Sidecar functionality under "Options > General > Importing & Tagging". There may also be some tags that can't be saved in FLAC files, so use Sidecar file for those files as well. i.e. Enable Audio Sidecar files.
So you could just save all your new or changed Views, save all the tags you want to the FLAC files or Sidecar files if they can't be saved to the FLAC files, go back to your pre-error Library Backup that points to the external disk, update the Library database to point to the new location on the Drobo using RM&CF, and then import the Views and Update Library (from tags) for all affected files.
Option 2:Or, you could identify which Duplicates are the bad ones, if there is even a difference now that both duplicates play and are found via "Locate > On Disk (external)", and delete one of the duplicates from the Library, but not from the disk.
While the two records in the Library for the duplicates may look identical, they will have different File Keys, I suspect. MC uses File Keys to identify all file in the Library. You can view the integer value of the File Keys by adding an Expression column to a View and using the Expression "FileKey()" without quotes. See
https://wiki.jriver.com/index.php/File_Path_and_Identifier_Functions#FileKey.28.E2.80.A6.29 for more information.
If you are seeing an anomaly with the naming of one of the duplicates using the Rename function as I mentioned above, you should be able to decide if the files with low values of File Keys are the bad ones, or the files with high values (more recent files). Based on that, if you can find the range of File Key values that the bad files have, then you can create a View to show only that range, and then delete them from the Library. As always, if trying this method, backup your Library before you start so that you can get back to a known point if needed.