How far back should a Cumulative Flow Diagram ideally go?

[Andrew Martin]

I have a Kanban project on Jira. As it's Kanban, there is no time boxed work activities on it (i.e. sprints).

Given this, I'm curious to know if there is any recommended time period I should look back on for my Cumulative Flow Diagrams. My projects have been around since mid 2018. If I run a CFD on a filter that includes the entire project, I can obviously sub-filter it to show the last month, 3 months, 6 months etc.

But given the huge number of issues in the project, the look of the graph is completely different if I then change the original filter to show just stories created in the last year, or even stories created in the last month. These changes fundamentally change the slope and display of the diagram.

Including all the data in the project's history seems redundant given how far back it goes, but at the same time I want enough data for it to be representative of the team over a good period of time.

Is there any standard recommendation for a Kanban team as to how far back I should be looking to get a good, approximate view of team progress? I appreciate this is almost entirely subjective, but I want to avoid simply choosing time periods that make the graph look the prettiest - I want to make sure I'm being consistent and looking at a true representation of how the team and our process is working.