Many thanks for your comprehensive response and your constructive feedback in the past.
Unfortunately, there are some apparent misconceptions which I need to address for the wider benefit of the forum community.
Your selection of Route 6 is interesting in the context of the missing WTT’s to which you refer, as Metroline have not produced a dedicated Boxing Day schedule, though a Christmas Eve one was actually produced. Nearly all 24 hour routes have had a confirmed schedule supplied by operators for Christmas Eve, slightly fewer for Boxing Day,
Where schedules are missing, as you correctly suggest, the consequent default we would follow is to use the last Saturday bus or first Sunday bus of the standard “day” timetable ie exclude anything within the N6 file. Answers to your questions are consequently Q1. (i) and Q2 (i). However, Journey Planner itself is actually returning 0535 as a first journey. 24 hour routes were effectively released in one go when all timetables were ready in JP rather than a piecemeal approach.
Every single 24 hour route, either where schedules have been supplied by operators, or customised as described, has been checked in Journey Planner, and by association the API. N prefixed routes have been suppressed entirely.
Looking at the detail, I think I have established the limitations of the TransXChange files, compared to the API, which has been updated each day this week in comparison to the weekly TXC uploads, in that they are potentially truncating these timetables at midnight. This would appear peculiar as such an issue would more logically be commonplace for any route which has journeys in the early hours of the following day. This does not appear to be the case, and there has never been a suggestion that this has happened in previous Christmas datasets (this is the twelfth TXC one produced, or in standard timetables). Is it then down to how they are being interpreted by users?. There is no question of journeys being blocked as you allude to, other than as explained above to release data in one set.
We very much support your suggestion of a detailed list of last buses at least for 24 hour routes, but, as you acknowledge, the festival travel information is not drafted by our team. However, the point to underline is that Journey Planner and the API have been thoroughly tested and are complete, as well as being updated far more frequently.