The amount of heavy elements present in a star when it formed will be neglible to the amount that will be created over time through fusion.
You can actually detect this through spectroscopy because the initial amount of metals will be present in the outer layer of the star. Heavy elements made through fusion will be mostly in the core.
The reason stars formed from primordial gas, i.e. only consisting of hydrogen and helium, is that such a gas will fragment less as it cools and collapses. Less fragmentation means heavier stars.
I only have a high level knowledge of the process though.