To your first question, the answer is yes. You could take any approved molecule and apply a new formulation and get exclusivity on it. There are many companies that are trying to do just that.
Of course, your new formulation actually has to add some value (1 tablet per day instead of 1 table three times per day).
To your second point, the Mucinex example is "taking an old drug with no clinical data and getting them back into the mainstream". The difference is that instead of it just being the active ingredient, it's a time released version of the active ingredient. Prior to Mucinex being approved, there were unapproved versions of long-acting guifenesin out on the market.
You're right it's not exactly the same as "no one has tested this drug at all", but rather "no one has tested this formulation of this drug".
Of course, your new formulation actually has to add some value (1 tablet per day instead of 1 table three times per day).
To your second point, the Mucinex example is "taking an old drug with no clinical data and getting them back into the mainstream". The difference is that instead of it just being the active ingredient, it's a time released version of the active ingredient. Prior to Mucinex being approved, there were unapproved versions of long-acting guifenesin out on the market.
You're right it's not exactly the same as "no one has tested this drug at all", but rather "no one has tested this formulation of this drug".