Why do the figures change?
New information can revise an estimate.
Statistics can change when more records become available or a method improves. A provisional estimate should be read with that possibility in mind.
When a release revises earlier periods, compare the new figures on a consistent basis. Mixing a revised estimate with an older release can change the apparent trend.
A projection describes what would happen under stated assumptions. A forecast is an estimate of what may happen. Neither is an observed count of future arrivals.
Does a projection prove how many people will arrive?
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No. It depends on assumptions and must remain labelled as a projection.