This is very insightful, thank you for the response.
On the "cul-de-sac" issue, just to clarify, when a late change happens (e.g., a part-time teacher's available days shift in June), how do you typically resolve that now? Do you literally have to unravel large chunks of the grid manually, or does Timetabler give you any smart recommendations on the least-disruptive changes?
Also, more on Options for Year 9 etc, does the rest of the school generally get resolved first then GCSE options take residual resources?