You can use premium assets across multiple projects.
However, Asset Credits are charged based on a 'per asset per project' basis.
This means that you can use the same asset multiple times across the same project and it will be considered as 1 asset credit.
But if you use the same asset across different projects, then the asset will be charged per project.
eg: If you use the same premium video asset across 3 projects, it will be charged as 3 asset credits used.
Note: Duplicating the same project multiple time will be considered as different projects.