When Edmund is given the red wine, he opens the cupboard door and throws it in, spilling it all over the floor. Elizabeth knocks at the door and it cuts to a shot of Percy knocking in reply to the knock at the door. When it cuts back, the drink on the floor has gone.
Wearing a crucifix, or crucifixes all over one's clothes as the Whiteadders do, would be an overt sign of Catholicism, not Puritanism; also, nobody in Elizabethan England would flaunt their Catholicism like this without risking serious punishment.
When Blackadder explains the kind of person he needs at his party Percy suggests Cardinal Wolsey. By the time Elizabeth came to the throne, Cardinal Wolsey was long dead, having died during the reign of her father Henry VIII.
When Baldrick is told to "get the door", and carries out this instruction by removing the front door from its hinges and taking it to Blackadder, the front door is visible, still in its frame, over the door that Baldrick is presenting to Blackadder.
The wall wobbles when Lady Whiteadder shuts the door when leaving after Blackadder gets drunk.
Edmund threatens to call the 'police' on Percy but the entire concept of a police force wouldn't even exist until the eighteenth century.
During the turnip dinner we are expected to believe that Blackadder twice kicks Percy under the table. Given that they are at opposite ends of the table this is not credible.