As for the P3 and below, they are absolutely a debt of some kind. They are actually IOUs given by the development team to the users. We know that most of them will never be repaid.

In my experience, there are two efficient strategies to eliminate this debt: constant refactoring supported by tests and bundling bugs in an area with new work in the same area.

I like the idea of making the bug visible in the code or in the tests. It may be interesting to maintain a list of failing tests rather than bugs reports !

I would propose at least two things:
(1) check if the users care and agree that x units of capacity will be used in each iteration to pay down some of the debt, and
(2) create tests for P3s and lower wherever possible to at least move the information from the bug logs into your code.

Assuming it is dirt-cheap to write tests, the second one means that a developer working on related code can see the associated tests when they are also cheapest to address. This makes the investment in fixing P3s as low as possible.

One related question:
- Would you be able to provide a similar graphic with three columns (P1, P2, P3-and-lower) showing number of bugs closed in the last 6 months?

César.