Is not probable, but not impossible

In theory a soldier or fishermen could have accidentally killed the first bird and reassign the tag at the sea, but I think that we could safely discard that because in that case, the female would have changed its nest location suddenly that year. Even more strange, would have changed its partner also.

To re-tag a bird that also occupy the same nest as the first bird, we would need typically to do it in the nest area. That would need a scientist (typically as the number of people visiting those remote places is scarce), and one with a known name. A daughter of the bird could have occupied the empty nest spot.

But this is all speculation, of course. Marks on the bird could provide the required info. With mammals with spots is much easier, each animal has a different pattern. With Albatross, the valid patterns could be on the face leg scales or in some scars.

After death the bones could be read also for confirm the age, but DNA analysis should be the weapon of choice in this cases.