I have a couple of shorex booked, some booked in November 2023 and one booked last night. The verbage is identical on both. I think the para you are referring to is this one:
If your tour is cancelled more than 3 days prior to cruise departure, a refund will be issued to the credit card that was used in the original transaction. Cancellations cannot be made online during the 3-day period prior to cruise departure. For cancellations made onboard the ship, a credit, less any cancellation fee, will be applied to your shipboard account. If the credit is not fully utilized during the cruise, the balance will be issued to your registered credit card at the end of the voyage.
This makes sense as it relates to cancellations made on board and being unable to cancel them for the three days prior to departure. If you embark and then cancel two or more excursions (one or more of which is scheduled within the first three days of sailing and therefore subject to cancellation fees), then you will get a OBC for the shorex which are more than 3 days from cancellation date but any within the first 3 days will be deducted.
So you as soon as you embark you cancel excursion for day2, day5 and day 8, then the credit less the cancellation fee for day 2. will be applied to your onboard account.
At least I think that is what they intend...??