Here are the instructions to point Lightroom to the external drive for specific folders:
It's the folders on the original drive, not the external drive, that should have the question marks in Lightroom.
If I were you, I'd strongly consider doing the move in your operating system this way (see "Part 2 — Updating Folder Location") in the future instead of doing the move inside of Lightroom.
Better yet, don't put photos on the internal drive of the laptop in the first place, future photos should be imported directly to the external drive (unless you are travelling with the laptop but no external disk with you, and so the only drive you have for the photos is the internal drive).
Thanks dj_paige! I should have mentioned that the folders on the original drive (which are no longer there, they're on the external) also do not have question marks in Lightroom. In fact, those folders aren't even shown on the original drive in LR (like the image in Part 1, Figure 4 of the link you provided). If they were I think I'd understand how to do this better. How do I go about pointing to folders that don't show up in LR either on the internal drive, or the external drive, but which contain folders with files that are part of the catalogue that I've worked with at some point?
Thanks for the resource on how to do the move for the future. I can't quite see always having all photos on the external drives, since I use the laptop quite a bit in places where the external just isn't feasible. That is a suggestion to consider, however.
If all you did was to move the photos using your operating system, there's no reason that the folders on the original drive AS SEEN IN LIGHTROOM would disappear. So I have to ask, did you do something to these folders in Lightroom?
Please try this: in Lightroom, click on All Photographs, and then find one of these photos that has been moved using the Filter Bar and searching by file name. If you find it (you should unless something else has happened) then right-click on it and select "Go To Folder In Library". This should highlight the folder in the Lightroom Folder Panel (you may have to scroll up or down to find the highlighted folder). Report the results, do you find the folder in Lightroom via this method? Is there a question mark on the folder in the Lightroom Folder Panel? Is this the folder you expect?
I performed the test you suggested, and was able to locate some of the photos in All Photographs which are in a folder marked with a question mark. These happen to be on an external drive with a different letter than the one I currently have plugged in is mapped to. I have 3 complete duplicate copies of all photos as my backup system, one on each external drive. In fact, there are 4 different drive letters shown in the Folders window on the left in Lightroom. Each has several folders with question marks, but none of the drives have all of the Year folders in one place. It seems that I have accessed a few folders from each drive over the years, so Lightroom is expecting some to be on different drive letters than others. In the end, I would like to end up with all the Year folders shown on one drive.
So, the question now becomes is there anyway to somehow consolidate these all under a single drive letter? I briefly looked into changing drive letter on an external drive in Windows. It seems straight forward but comes with this warning: "some programs that rely on drive letters might not run correctly after drive letter is changed", so I wanted to be sure before proceeding. It seems Lightroom might be in that category.
To answer your first question in the previous response, after having looked through the right-click menu options, it is possible I chose "Remove" on the folders that were no longer in the original drive at some point. I cannot recall since it has been a while.
Thanks again for offering up your time to wade through these waters.
You consolidate all the folders on a single drive by following the instructions in the document that I linked to.
If all the photos are now on drive Y according to your operating system, then for each folder in Lightroom with a question mark, point Lightroom to the proper location on drive Y.
Removing the folders from Lightroom is not a solution, it is a choice which would cause all of your work on these photos to be lost.
Success! Many thanks again dj_paige...