Upgrade scenarios in the main app, not the selection app?

Old scenarios get upgraded in the inputs selection app. This is done by assigning the model-version string as a class and then applying methods against that class. The class is then updated to the next model-version number and new methods are applied. And so on.

Dev runs do not get an app_version in params though, they just get the string 'dev'. Therefore they don't get upgraded and it borks the app.

As @tomjemmett points out:

so far all our changes to the params over time have been quite simple upgrades from a->b. Might there ever be a case where that isnt true?
I suspect the issue here is that dev scenarios don’t upgrade, so they have the wrong ndg values now
So my thought is: should the parameter upgrading be in the inputs app rather than the selection app?
Should the dev version be something more like app_version = vX.Y.Z, but have a is_dev: true flag

Compare where scenario parameter upgrades run in the inputs selection app versus the main inputs app, starting with the app_version handling described in the issue. Reproduce a dev scenario using app_version 'dev', then determine how it should receive the same parameter upgrades while preserving a development flag; done means dev scenarios no longer fail because their ndg values are outdated.