In Jira, I've found that a Project best maps to a software product. This enables more efficient use of the Releases and Components functionality. By using the Fix Version field on issues, you can target work toward a particular Release and then use the Releases view to track progress. Internally, to your organization, you may treat a release as a project, but the use of the Fix Version field, along with labels and issue linking, is what you would use for monitoring scope and tracking progress.
By using a single Jira project, you also enable the use of Releases to track Affected Versions. Often used for bugs, this lets you track which released versions a bug is found in. If you split the work up across multiple Jira projects, this wouldn't be possible.