Last year I ordered new bands, but I was thinking of reusing them this year as I know you are supposed to be able to reuse them over and over again.
Do they just link the info to your existing bands as long as they are still listed on MDE? I was going to start decorating the ones I have, so I just wanted to make sure that there would be no issues when we arrive. TIA 
I just returned from Disney World Last night, and was able to re-use my magic band on my most recent trip, which I purchased last year. I had no problems entering the park or any of the rides. (Considering the cost if you purchase them yourself, I would definitely re-use them If I could)
The Disney Cast members in the gift shop told me that the Magic Bands are good for --2 years--. Unfortunately, the batteries die in them after that time frame.
I found that once I linked my new park ticket to My Disney Experience, it worked fine. And as I activated my ticket at guest services (I was staying at the Dolphin, and they have a spot there to buy tickets), they were able to check that my band was working).
So long as you make sure you link your current Disney tickets and Hotel reservation to your My Disney Experience, you should be fine. That said, locations that sell the magic bands --should-- be able to test your bands for you to make sure they are connected properly and working well for you.
Sorcerer Mickey
Your info will be linked to all "active" bands listed on your account. (If you haven't actually "deactivated" your band, it's still active.)
From the Walt Disney World website:
Q. Can I reuse my MagicBand or card the next time I visit Walt Disney World Resort?
A. Yes. If you have a MagicBand or card that you like, and it is in working condition, you can continue to use it when you return to Walt Disney World Resort.
If you have multiple MagicBands or cards, you can manage which ones are active in the MagicBand section of My Profile.
Q. I have multiple MagicBands or cards. How do I manage them?
A. You manage your MagicBands or cards in the MagicBand section of My Profile. For example, you are able to:
*Activate or deactivate MagicBands or cards
*Report a MagicBand or card as lost
*Customize MagicBands before they are shipped
Multiple MagicBands or cards can be assigned to a single person, so activating a new MagicBand or card does not mean that you must deactivate an existing MagicBand or card. All active MagicBands or cards assigned to a person have access to the benefits and entitlements for that person. Adding a new MagicBand or card does not add new entitlements, such as additional theme park admissions.
If you require additional assistance managing your MagicBands or cards, please contact us or visit any Guest Relations location at Walt Disney World Resort.
~ Barb ~