Continuity mistake: The package Steve received from Mailbox is briefly visible before Mailbox comes in. You can also see a crew member's hand holding the package as Steve grabs it.
Blue's Clues (1996)
1 continuity mistake in season 1 - chronological order
Starring: Aleisha Allen, Steve Burns, Seth O'Hickory, Traci Paige Johnson
Blue Wants to Play a Game - S1-E12
Other mistake: The jigsaw puzzle Steve and Blue help Shovel and Pail with has a picture of everyone playing musical chairs from the Mailbox's Birthday episode, but Steve suddenly isn't in the puzzle. He played musical chairs, so he should've been in the puzzle.
Steve Gets the Sniffles - S2-E1
Trivia: During a mailtime segment, there's a rare Blue's Clues poster visible.