What does -1 signify in system.schema_version?
-1 means the module is not installed. Updates are only run on installed modules, which is why any update in a module with a status of -1 will not run. If the module is coded properly, when the module is installed, it will be installed in the same level as if all updates had been applied, as updates are used to bring the database in line with the current definition of it in hook_schema().