certain disease in the entire population, age standardized mortality rate (ASMR) is much better than crude rate because ASMR takes into account the age structure of the population. In COVID vaccination data, it becomes complicated because the vaccine rolling out was by age. The other likely source of discrepancies is that you need to consider when the death occurs. For example if someone died 5 days after his first shot, is he considered vaccinated or unvaccinated? There must be a pre-defined criteria to process this data. The back of envelope calculation you did is a very crude mortality rate, and is unlikely to be the same as the ones released by governments (UK NHS , Ontario Science table or CDC).