It's based on our historical experience maintaining versions (or, at minimum, trying to not change the core DSL such that older formulae continue to work): we g

It's based on our historical experience maintaining versions (or, at minimum, trying to not change the core DSL such that older formulae continue to work): we get an order of magnitude more requests for updates than requests for older versions, and even fewer specific complaints about breakage. When a particular package (or version) is widely adopted and difficult to migrate away from (like versions of LLVM, Postgres, or Python), we provide `@`-discriminated versions to allow people to migrate at their own pace. If there's a particular formula you want versioned that we don't currently, please open an issue so that we can discuss it!