One of our clients back at McKinsey in the 1990s used to say that "the paper in McKinsey documents is always warm", i.e., they came of the printer only minutes before the meeting. Now that documents/presentations are all in digital form there is even greater opportunity to make last minute changes, especially if you travel by taxi to the meeting.
It comes at a price though. First of all, last minute analysis is prone to mistakes. But secondly: "frankensteining" quickly a chart into a presentation might break that super professional and impeccable look of the presentation.
If the change does not involve the correction of a major error, it might be better to make that missing point verbally.