Have an interesting circumstance. If you are using an Agile/Scrum approach what I have seen historically is that each dev team has a backlog. Different projects funnel stories into the one team backlog. This allows you to clearly see the amount of work the team is tasked with doing. My current client insists on having a backlog for each project and sprint, so there is sort of a Cartesian product of backlogs.
I can understand how it may make project management activities easier, but it has only served to confuse me as far as understanding what work the team is currently and future tasked with. I mentioned my questions, but the client assures me they know Agile and this is how Agile is done. It has been interesting to compare this approach to others I have seen. So far it seems to muddle the concept of a sprint as sprints have no start and end date, they end when all the work for the project/sprint backlog is done. If it works better than one team backlog I’ll be down with it and waiting to see how it all turns out to make that determination.