You can purchase
DCL's trip insurance up until the final payment due date. They do have a pre-existing condition exclusion provision. Briefly, from their brochure, exclusions are:
1. any injury occurring prior to and including the effective date of insurance (i.e. effective date of your Trip Cancellation coverage or, if no Trip Cancellation coverage is purchased, your trip departure date).;
2. any illness occurring during the 60 days prior to and including the effective date of insurance for which treatment by a licensed physician has been sought or advised or for which symptoms exist which would cause a prudent person to seek diagnosis, care or treatment. However, if the condition is controlled (not exhibiting symptoms or requiring an adjustment of treatment or medication) throughout the 60 day period by the taking of prescription drugs or medications and travel restrictions are not advised by a licensed physician, then the medical condition will not be considered a Pre-existing condition.
So, without being accused of practicing law; my interpretation (corroborated by a DCL representative) is that you can be taking prescription medication for a condition; and as long as you are not treated for said condition in the 120 day (or so) period before your cruise, it is not considered a pre-existing condition and would be covered. Of course there are general program exclusions that are defined in the DCL Vacation Protection Plan brochure. Additionally, benefits would be coordinated with any other secondary converage you may have.
All in all, the plan provisions seem to be fair and reasonably priced. I only would have been able to save less than $40 with an outside insurer. Since I didn't want to purchase the insurance at the time of booking (good thing since I had to change the cruise several times already), I'm happy to be able to pick it up when I make my last payment. Good Luck.