Its not likely to succeed, because the drift of references of a model type tends to be positive or negative, not both, so they'd not likely cancel each other out.
Further testing to 1mV precision, you won't detect the drift, its typically in the uV range at the least. If a reference had an annual 30ppm + or - drift, [ the good news is internal drift eventually plateaus with age, so the rate of change will eventually stabilize and be less than the quoted spec], say on your 5V reference as example, that would be 150uV per year; it can take 10 years of continuous drift in the same amplitude and direction before it would register 1mV change. In that same 10 years, the rate of change will also drop, so the drift of 30ppm will also decrease, and this offsets the likelihood that the actual value of the reference is not 5.000 000V to begin with, so that it would really take 10 years to register a 1mV change.