A prototype is built to get an answer. A product needs to give the same answer every time. That difference changes the kind of decisions you make.
Plan alternatives for parts
In hardware projects, sourcing is part of the design. If one critical IC can only be found through one path, the product carries unnecessary risk.
Design the test path early
Even a simple test pad can make production debugging much faster. Testability is usually cheap to add early and expensive to add late.