It depends on the amount of fudging you're willing to do.
Let's use format 1 for a moment. It's a list only of the directories in the tarball.
The fields relevant to each entry in the list tarball are: mtime(seconds+nsecs), device, inode.
In later incremental passes, if the device/inode fields no longer match, or if the mtime has moved backwards, ALL the files in the directory will be added to the incremental tarball. If the device/inode match, and mtime is the same or greater, it will pick up all new files greater than or equal to the mtime (The equal-to part matters for filesystems with low mtime resolution, otherwise files might be skipped).
Format 2 extended this via the Dumpdir format, which complicates it,
mostly adding cases where files aren't backed up as they came with an older mtime.
So, given a tarball, is it possible to recreate a snapshot file? Yes, but it's messy, and you'll probably miss some files. There is
--no-check-device which skips the device check, but the directory inodes are the big risk.