It is not unusual to find that the guide you have taken days to develop and hours to practice is not quite right. You should hold a quick debrief after every interview (or at least after the first five interviews) to determine what works in your guide and what doesn't. These sessions should be held with all of the team that took part in the interviews. Are the questions you wrote understandable to the customers, or are customers sometimes confused by what you are asking? Does the flow of the questions and the transitions make sense, or do you need to change them? Do the questions yield the type of information you are looking to get from the customer, or do you end up with superficial responses that are not actionable by the project team at the conclusion of the interviews?

If you are handling multiple teams, make sure that you coordinate with the other teams and discuss whether they had the same issues with their interviews. Regardless of whether they did, if you change one discussion guide, make sure all the discussion guides are changed to better ensure future consistency.