I see the logic with this truncated sync: it saves time, but I disagree with it. Such an implicit effect can be dangerous, and surprise the user. If you want to be consistent, then you should also prune the old data based on the graph view period.
One solution could be two settings
- One for graph view period
- Another one for data retention period, also used for syncing (another implicit thing, I admit)
Such an approach would make it clear to the user what to expect.