I believe that planning succeeds better than just ESP. If you need parts, you always need to have at least two suppliers for each part and hopefully three or more. Why? Just for the reasons you stated. In a crunch, you need options. If you have a sorted list of suppliers, you can quickly find a replacement source for a while if your primary source experiences unexpected difficulties.
It is all about good risk management and planning.
Just my opinion.
Blog Make a Frequency Plan Tom Burke 17 comments When designing a printed circuit board, you should develop a frequency plan, something that can be easily overlooked. A frequency plan should be one of your first steps ...