Are all Show() calls guarenteed to be successful after the first time IsReady() returns true?

I’m new to UnityEngine.Advertisements, and am having trouble understanding the API. Kindly bear with my questions.

I’ve got 2 scenes: mainmenu, and game

mainmenu will be the first scene unity plays when the application is run.

Scripts in game must be allowed to call Advertisements.Show() successfully, at any given moment.

The game scene will be loaded from mainmenu, but can only do so when Advertisements.IsReady() returns true.

When in game, are all Advertisements.Show() calls guaranteed to be successful?
As guarenteed as 1+1=2?

No, you need to call IsReady() to find out if there are ads available. Situation could e.g. be that the SDK need to fetch new ads from backend.

If IsReady() returns false, Show() will simply not do anything.

/Rasmus