Music folders/files are added to iTunes Media folder instead of Music subdirectory

Thanks for that link! I was able to ferret out the solution among the detailed info in that article. Basically, somehow my iTunes library forgot that it was using the "iTunes 9 & later" folder layout (see image below) as a result of migrating from one drive to another. It had reverted to the "iTunes 8 & earlier" layout, which led to music files being organized improperly as described in my original post.

This one line in the linked article ended up being the key step to fixing my issue:

You can switch the library from the old layout to the new one using File > Library > Organize Library... > Rearrange files in the folder "<Media Folder>". This option is not available if the library is already in the new layout.

Sure enough, the option was unchecked despite the fact that the new layout had been correctly in use pre-migration. Thanks again for your help!

Thanks for your response! To which details are you referring me in the linked support article specifically, please?

I see from the Preferences image you copy/pasted that the iTunes Media folder location is different. It specifies a path that is typical for the default installation options on the main C: drive. However, I have a large library and don't want to waste SSD capacity on media files that tend to consume space quickly. I had used a similar alternate location (I:\iTunes\iTunes Music\) successfully for years prior to this migration. Only since this move have I noticed the undesired behavior when adding new music files, described in my original post above.