When Garak and Sisko first meet in Garak's shop to discuss manufacturing evidence, a gap can be seen in Garak's neck ridges on the right side, just above the scales.
When Sisko has his uniform jacket open to reveal his captain's vest, the jacket appears much bulkier than usual. This is because the vest is never actually worn under the jacket, but just appears whenever the jacket is opened or removed.
Ambassador Vreenak leaves the station knowing the data rod is a forgery. Later his vessel is destroyed and presumably he is killed. He may have had time to transmit his knowledge of the Federation attempting to entice the Romulans into the war to Romulan headquarters before he died, but from the results, presumably he did not. No measures are shown to prevent this critical high value information leak.
After the Dominion has taken Betazed, Kira asserts that puts them in a position to take Vulcan and Alpha Centauri. Both planets are known to be very close to Earth (Alpha Centauri is a real star location approximately 4.37 light years from Earth's solar system, a very short distance for warp-capable civilizations), the Federation's capital, yet no mention is made of Earth being in a vulnerable position.
Dr. Bashir asserts that if the Romulans were brought into the war on their side, then they could finally go on the offensive. The joint Starfleet/Klingon task force went on the offensive in the "Favor the Bold"/"Sacrifice of Angels" 2-parter earlier in the season.