"are they made available to the open market? or offered...

"are they made available to the open market? or offered privately to instos?"

Nuts

New shares cannot just be "made available to the open market". This would be an entirely new capital raising and require a prospectus and considerable time delay.

I firmly believe that a shortfall in the SPP is unlikely but that said, the instos would soak up the balance in a "private placement".

Effectively that means retail investors, whether existing shareholders or not can only purchase on market post the closing date of the SPP.

Hope that helps.