Not if proving so is more expensive to do than not. Reliability is only a means. Not the end. Also the human parts of the business would need to be simplified in order to model them. If deviate from the model that could invalidate it.
Savvy processors recognize the immutability of each API version published to Merchants, along with how long each must be supported, and employ FP techniques both in design and implementation of their Merchant gateways.
Of course, the each bank's mainframes "on the rails" do not change unless absolutely necessary (and many times not even then).