There is no simple "the board". A product, which may be largely a circuit board, goes thru several steps.
Most of the time I design the circuit for what we think we want the product to do, but the first version is a bench test board. This isn't even pretending to have the final mechanical form. It is a board with as much space as it takes to be able to probe around, make edits if necessary, etc. This is usually a rectangular board with rubber feet on the bottom in the corners. The circuit is what is intended for production but often with some extra debug facilities. For example, unused processor pins are brought out to labeled pads instead of just ending at the processor. There might be extra LEDs, or maybe a serial port even if the final unit won't have one. Deliberate labeled test points are added for various intermediate nets that might be useful to connect to, look at with a scope, feed a signal into, etc. There may be jumpers in a few places to disconnect parts of the circuit. The point of this board is to verify the circuit and get the basic firmware up and running.
In unusual cases when I think a circuit is risky or it's hard to know what is really needed, I may test just a small piece on one of those plug strip breadboards. For example, a while ago I had to make a product receive and process ultrasound signals, but with very low current. You can read all the datasheets there are, but for something like this it takes real experimentation to find out what gain is good enough, how little bandwidth can be gotten away with in reality, and whether some of the extra low current tricks really work as expected. Transistor datasheets generally don't tell you what the part characteristics are with only a few µA thru it. Sometimes you just have to try stuff. Fortunately that is unusual, and can be limited to a specific sub-circuit. By the way, I got the ultrasound front end amplifier down to 35 µA at 3 V quiescient current, and a gain of a few 1000 at 40 kHz, all with discrete transistors. That took some experimenting.
After the first bench test board, the customer inevitably wants something different than envisioned at first, you find little things you may want different, etc. The next version usually takes the mechanical constraints into account, so is probably a smaller more crammed board. You'd think that was it, but rarely is the second version ready to ship. That's generally not because of circuit problems, but mostly because now more people get to see it, smell it, touch it, feel it, and otherwise muck around with it. These people all have their own opinions on details of the product, and a few things will change.
The third version can sometimes be ready for production, but usually it takes one or two more revs before everyone is happy or has given in, some part got moved because the original dookicky this thing was supposed to work with got obsoleted in the two years since someone dreamed up the product idea, etc. I'd say total of 4 or 5 versions of the board is the most likely, more for large organizations that pride themselves on process and procedures.