They say the standard version is all natural but the low salt version is fortified. Don’t know why the ingredients say that as the nutritional info is the normal place.
Nutritional information Vegemite is a source of B vitamins, specifically thiamine, riboflavin, niacin and folate (B1, B2, B3 and B9, respectively). The base version contains no vitamin B12 (cobalamin) although both vitamin B6 (pyridoxine) and vitamin B12 are added to the low-salt formulation.[38] The main ingredient of Vegemite is yeast extract, which contains a high concentration of glutamic acid, the source of Vegemite's umami flavour. Vegemite does not contain any fat, added sugar or animal content. It contains gluten (a composite of storage proteins) as the yeast is derived from brewing.[39] One 5 gram serving contains 173 mg of sodium, which is 8% of the recommended daily intake of sodium.[40][41] Australia only defines low salt foods, but by UK standards Vegemite is classified as a high salt content food.[42] A low-salt version of Vegemite was introduced in September 2014. It has a 25% reduction in sodium content. The low-salt version is also fortified with vitamin B6 and vitamin B12.[38]
For a person not part of the company to leap out and assert that a product does or doesn’t contain a substance is high risk. They take on the risk that the company may have been lying, may not support them etc. The company differentiates 2 of their products which leads to the thought that the classic is not fortified but unless the Vegemite comes out clarifies it, it is not a incontrovertible fact. They have been making it since 1923 which is well before added vitamins were a popular thing and I can say it tastes the same (as much as I can tell) since the 1950s. So on balance I think that they don’t fortify it.