You are using multiplication, which will likely not place you on an additive scale. What is the reduced mortality for your study patients on Drugs A, B, and C? Is your study prospective and are you using relative risks, time to event, or odds ratios. Are you controlling for any covariates?

What I was trying to get at is whether the reduced mortality from drug A, B, or C individually, from other studies, are coming from comparable patient samples as your sample. In particular, I doubt they are comparing a drug treatment group to a healthy comparison group without any risk for ASCVD. Also, was their study design comparable, did they prospectively follow patients and report relative risks or odds ratios based on proportional hazards regression (time to event analyses), which likely controlled for covariates if treatment assignment was not randomized. Lastly, is it possible to determine the background risk, for I am assuming, a cardiac event related mortality in the comparison studies that examined the effectiveness of drugs A or B or C. If the background risk is not comparable to your study or if they had a different study design or controlled for covariates, or had randomization, or a comparison group at risk for ASCVD then in my world, a calculation for additive effects would be VERY biased and not conscientiously appropriate to report without a lengthy limitations clause.

But it might be fun to make this calculation, just for the sake of entertainment!