RunTime and StartUp versions. And on the fly migration

[zzapara]

During migration on startup we discover version like this:

where current is

So if we will have RunTimeVersion it will update to this version.

And in this case where is role of OnTheFly migration where we use BsonSerialazer to serialize document on fly to runtime version? If all documents will be updated to runtime version on the start

[zzapara]

Or on fly migration allow you to run real migration in background and in runtime get latest version of document?

[zzapara]

mistake