DCL ships, like most cruise ships, sail with all staterooms occupied most of the time. There may be some variance because maybe not every bed is used, but really there just isn't that much variation. We've been on, for example, the Wonder when it was about as full as it ever sails, and it was perfectly fine and didn't really seem extra crowded.
Now, in the ports you may see some variance, but no, I wouldn't think early May is going to be hugely busy. You will probably not see completely full ports like you would over Christmas or spring break.
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