In Canada, I was able to take my whole insurance policy, which includes COVID-19 coverage since it was bought way back in 2018, to my rescheduled cruise in summer 2021! (Everything I booked was refundable to cash or future travel vouchers.) I saved loads of money not having to buy insurance again ($2000!) and it will have rates from 2018 AND COVID-19 protection on the future vacation. I love premium insurance policies when they are flexible like that. And I'm very grateful we opted for the more expensive, more flexible and wide-covering policy.
If people here are referring to the 125% future travel credit, it's only on the cruise fare, not the port taxes. You'll have to look at your invoice to see what the price was before tax, then add 25% to that number.
Our first cruise was $5500 for 11 nights. Our replacement 2021 cruise will be $11,300 for 11 nights... ugh. Same room, even. But we booked opening day for the first one, and now had to pay prevailing rates on the new one, though I presume the new one was still around $11,000 to begin with. That 25% doesn't help us much, as we'll be saving up for the next year to pay the difference. Yikes!