After Sherlock runs after Major Sholto and John decides to follow, the shot that has John walking through the guests shows Mary in the background having already left the table. Whereas, the next shot shows her just leaving the table.
When Mary and John are greeting guests at the reception, they greet the same couple twice - an elderly woman in a large white hat and bright pink jacket and a man in a light gray suit.
During Irene Adler's cameo, the position of her hand on Sherlock's face changes between shots.
When Sherlock and Watson are in jail, Sherlock's right arm is hanging by his side. When the man enters , Sherlock's arm jumps from hanging to resting on his chest between shots.
After Sherlock shows Janine his dance moves, they are talking and Sherlock's hands alternate between behind or in front of his body.
Sherlock refers to Bainbridge as a Grenadier, but the guard uniforms shown, including his, are of the Welsh Guards. One can tell by the collar emblem (leek) and by the grouping of the tunic buttons in fives. (Both Welsh and Grenadier guards are of the Household Division infantry; neither are "Beefeaters," which nickname refers to the Yeomen Warders of the Tower.)
As they start the stag night pub crawl Sherlock produces two glass containers - measuring kit from a chemistry lab. Sherlock says that the glasses should be filled to 473.2 milliliters. That is equivalent to one US Pint. However the regular measure in UK pubs and bars is the UK (Imperial measure) Pint, 568.3 ml.
When Sherlock says, "Vatican Cameos," at the wedding, only John gets alarmed while Major Sholto doesn't. Being a man from the army, he should have known its meaning; even more a reason that Sherlock calls him a man obsessed with security.
However, it was code-word only Sherlock and Watson knew and wouldn't mean anything for the outsiders. Nothing indicates it to be a military code.
Modern smart-phones have a proximity sensor that turns off the screen only when you use the phone to call people. When Sherlock and Mycroft are talking, we can see that the touch sensitive buttons of Mycroft's phone go on and off between frames.
Major Sholto, upon entering the wedding venue, would remove his beret. British Army personnel are trained to remove their headdress as soon as they are indoors.
John greets Major Sholto with a salute, but would not do so out of uniform. John would come to attention and Major Sholto, being correctly uniformed, would salute in return.