(CNN) Puerto Rico's true death toll from Hurricane Maria remains elusive as the storm's one-year anniversary approaches.

on Tuesday after maintaining for months that 64 people had died as a result of the storm. The island government raised the official death toll to 2,975 on Tuesday after maintaining for months that 64 people had died as a result of the storm.

But the higher figure, based on the findings of researchers from George Washington University in a study commissioned by the US commonwealth's government, is only an approximation, not a concrete list of names, according to Gov. Ricardo Rossello.

"This number can change," Rossello said. "It could be less, it could be more, as time passes."

Here's how the official death toll has changed since the storm touched down September 20 as a Category 4 hurricane: