Resolving Files and data moved to SD Card not scanned by Android
Files not recognized by android can be resolved by following ways:
Install another application that can search through smartphone for music, photos, text and other type of files.
Different music players, picture and other text processing apps have option of rescan library to search the file system.
Check the file explorer from computer system and view the contents of SD card and select and copy the files to the file path on your internal storage like storage/emulated/0/Android/data/com.google.android.music, storage/emulated/0/Android/data/com.google.android.photo. Then close and restart Google Play Music and go into the menu and select Refresh. Then your music should show up. The file path may be slightly different depending on the mobile device, but user can check in the subfolder com.google.android.music
Music player only scans songs that are in the android internal media database.
Android has a buildin service that scans the filesystem for media file (photo, music, and video) and transfer this info into the media database. It also depends upon android version and smartphone manufacturer. Media scanner has not been restarted yet and files have been transferred via usb, it may be helpful to dismount the sd card and remount it as it will initialize the media scanner.
Make sure that all your songs are in a folder without a .nomedia file. The .nomedia file is used to inform media apps not to scan any of the subdirectories of the folder where that file is located. This method is used by apps with video ads for example to prevent the video player from adding ads to its menus