Edge discounts in my experience cover all special event sales and programs in play throughout the year. I'd look specifically for lines of print that say otherwise, and expect them to be huge and noticeable, unlike other companies that might add it at a size 2 font at the bottom of their circulars stating the same.
Edge bonus for trade-ins are typically available through special trade-in promotions as well. Again, in my experience...its been used in all of the trade 3, 4, 5, get bonus % back in addition to the 10% edge cards add.
I don't even see the card as being the "Deal" as much as it's a cheaper subscription to Game Informer. Sadly, GI has gone a bit...bleh, as of late.
Most all of the trade-in and sale prices are upsold anyways, so the "extra" savings you get are just their inflated price brought down to what their actual trade-in and sale prices SHOULD have been from the start, a modest and reasonable profit instead of an ass-rape of a deal.