I'm working on a program that will update all the master pages for a given list of site collections with a banner at the top. I started off by querying each site and logging what master page each site uses. Then I am creating a custom master page for each type used. For example, for seattle.master, I create a customSeattle.master which is identical except for the banner at the top. I found a couple of sites using a master page "mwsdefaultv15.master". I'm guessing this is the master page for the Meeting Workspace site template.
The issue I am having is that when I navigate to these sites and look at the master page settings on the "/_layouts/15/ChangeSiteMasterPage.aspx" page, it shows seattle as the applied master page. Also in the drop down for master pages, mwsdefaultv15.master is not listed. If I navigate to the "/_catalogs/masterpage" directory, "mwsdefaultv15.master" is not there.
So what is going on here? If that mwsdefaultv15.master file doesn't exist, why isn't the site throwing an error. If it does exist, where is it? Do I need to update this master page, or can I update seattle.master if I want to add that banner?
Thanks