I see where I bought them. How can you tell if they are linked?
If you go into the Disney App, select the three lines button at the lower right. Then select "MagicBands and More" from the menu. This should show you all accounts you manage that have magic bands or media that is available. Select the person you wish to manage.
Depending upon how you selected it, selecting the Update line will go strait to managing all types, or selective the "..." will ask you what type (MB+/MB/Admission Card), then take you to the same managing all types and put you in the are you selected.
Now select the MangicBand+, if you are on MangicBand or Admission Card, and you should see all MB+ bands you have that are assigned to that specific person you are on. You'll need to go back and look at other managed people to see their bands.
If your band is here, then its linked to your account and should work barring any technical issues at WDW. But the device is now connected to your account forever more. And this is the same place where you you can Bluetooth pair it to your phone, change the lighting settings, and upgrade the firmware. And I highly recommend you update the firmware before you arrive at Disney.
Also, take note of the band number, should be a 12 digit number just below the picture of the band. That is it's unique ID number. All your media (bands and admission cards) have them.
Now you can go back to the three lines button at the lower right, and scroll to the bottom and select "My Profile". Then select "MagicBands & Cards" from the menu and you should see a list of every MB+/MB/Admission Card you've ever linked to your account again. That unique number should be listed there too. The little pictures may or may not be there, but its the number you're looking for. It should tell you it's active. If it does, you should be good.
Careful you don't accidently deactivate it.
Hope that helps