Think of ‘Magazine issues’ as something that is created within each ‘Magazine.'

This is to accommodate multiple ‘Magazines’.
For instance, if you have a ‘Monthly Magazine’ and an ‘Annual Magazine’ we can create two ‘Magazines’ (say, Monthly Magazine, Annual Magazine) and then add issues under each separately (e.g., June 2016, January 2005 under Monthly, and 2008, 2009, etc. under Annual ).

You can add a new magazine from Magazines on the admin panel and then click on View Issues to add each issue of that Magazine.