What sate are the iPads in during the first setup? What I have found is that they can not be setup at all prior to applying the profile settings in the DEP list in Systems Manager. If the iPad setup has been started in anyway prior to that step, a full wipe is needed. When it comes to the ABM/Configurator flow, it works a lot better when you are buying new devices that are automatically added to ABM and your default MDM. The configurator approach is a bit more intensive but you have to remember that up until about a year ago, there was no way to manually add previously purchased iOS devices. This, while being a bit of a pain setting up, is still much better than nothing at all.
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