Where's the flexibility in the Training Plans?

Zwift says their Training Plans are “flexible”. I did the 12 week Build Me Up last winter and am looking at what I want to do this winter. What frustrated me was there was no flexibility. If you did not get a ride done in the window they specified, it went away. If you do other activities in life, whether it be skiing, riding IRL, etc., you missed rides in the plan and they went away.

On most plans there is a spec of number of weeks with a range. I can’t find any plan that is not just the max number of weeks in that range. A 6-8 week plan is always 8 weeks, where does the 6 come from.

How does one get to do all the rides in a Training Plan yet have some flexibility on timing? What am I missing?