Most aircraft (RVSM) have dual digital ADC's that can be compared with the "steam guage" standby altimiter and A/S indicator to determine what is the likely faulty component/system.
Long before RVSM, as well.
Most aircraft with dual ADC's have mode failure indicators for disagreements between each others individual instruments and, on many, instrument transfer capabilities to isolate individal faulty indications.
Individual failures of an entire ADC are quite rare in my present type (L1011), in fact, I can't remember one...and I've been flying the same type for a
very long time.