Standards draw from practical experience, though often with a considerable time lag and not always with a uniform reasoned approach.
Depending upon the resources available (manhours, equipment and material) and the liability that you're prepared to assume, you can make the decision on whether to follow book values in any situation. You just have to make sure that your decision is appropriate to the circumstances.
You can stick any old thing together to demonstrate function to your own satisfaction. If You want it to work tomorrow or next week after some physical neglect and possible forgetfulness enter the picture, you've got to take some added precautions. If you expect another person to use it without untoward effects, the responsibility for assumed reliability and possible misapplication increases. Looking backwards to determine just what level of responsibility was assumed at a particular time of hardware development requires a paper trail that will not always be there. In that case, you might as well have stayed at home.......the 'book' values will outlast you.
RL