Can iTunes recognize a CD if it's in another folder in the Music folder?

Checked around and didn't find an exact version of this question:

Previously, I had my music stored in two places: my hard drive and an external drive.

I grew out of the external drive, so I moved the external files to a much larger external drive. I am now in the process of moving my hard drive files onto the new external drive.

However, I've run into my only major issue with Macs: the fact that identically named folders are replaced, rather than merged.

So for example, let's say I have a Wilco folder on my external drive. I also have a Wilco folder on my hard drive, with different albumss. I can't just move the hard drive folder onto the external drive, because I will lose half of my Wilco albums (all the external drive albums).

I recognize I can just do this one at a time, moving the albums into the Wilco folder on my hard drive. But I have several dozen GB of mp3s . . . it could take weeks.

Is there any quicker way to merge the two drives without deleting any files?

Steven