I have seen calcium ascorbate, dehydroascorbic acid and unidentified compounds sold as vitamin C. The human body can certainly use calcium ascorbate as C, but it causes precipitation in developers with carbonate. The dehydroascorbic acid is what results as ascorbic acid is oxidized in developers. The body converts ascorbic acid to this compound, which will pass the into the brain, there to be converted back to the vitamin by reactions our developers don't have (and we probably don't want them to have). Stay away from anything identified as "Ester C". It is easy to convert ascorbic acid to sodium ascorbate. 10 grams of ascorbic acid + 4.8 grams of sodium bicarbonate in a small amount of water make 11.25 grams of sodium ascorbate + a bunch of CO2 which fizzes away.
Whether you add sulfite or not, a developer containing Metol, sodium ascorbate and borax will have considerable activity. It is a good way to learn how much sulfite you really want for your purposes. If you didn't use any sulfite in D-76, you would find the synergism usually attributed to the MQ combination to be missing. Ascorbate takes the place of sulfite by replenishing the Metol instead of keeping the oxidized Metol from retarding the reaction, but seems not to have much ability to chew away the grain edges. That in itself gives no sure prediction of differences in graininess, because the structure of the grain clumps is different with and without sulfite in an ascorbate developer. A developer might first build up grain clumps and then dissolve their edges, or it might gradually build up groups of very tiny particles to reach a given density.
ascorbic and erythorbic acids are l-ascorcic acid and d-ascorbic acid, mirror images that our bodies can tell apart but our developers cannot.