In my experience magazines simply lie. Or let's be charitable, the editor *means* to do one thing and that is what they pay for, e.g half page. But then oh my goodness me whoops what a slip-up, the pesky art editor/designer/office scapegoat decided to change it at the last minute and it came out as a double-page spread - twice, once on the contents page.
My point? Very often we have no idea because we don't see where it goes (not least because we aren't told where it goes).
My question is, with Rights Managed, how much does Alamy actively check?