Planning is important, and with proper planning some pitfalls can be avoided. Revising a plan when new information is discovered is recommended in an attempt to keep everything flowing as smoothly as possible. I’m not sure what would happen that caused several different people to suddenly become unavailable (it seems like an assumption was made vs. confirmation of availability), however, having the insight to implement a plan B is appreciated. Dismissing the issue would cause a lot more problems than recognizing the issue and revising the plan as necessary.