I don't consider people who enter within the first week to be intruders. I'd say they are late arrivals. The first week is all about being introductory. Almost like an orientation or induction with new faces coming throughout. An intruder is someone who enters well and truly at a point where the game has passed it's beginning and there are established relationships and sides. Around a month into the series.
2003: The housemates entered the house throughout the first week. Everyone except the Square house five and Benjamin were latecomers. Jamie and Kim were the intruders.
2007: Susannah, Zoran and Billy were each also introduced on the second night. Not intruders, late comers.
2008: The three gatecrashers entered prior to an eviction occurring. In regards to the old school format of Big Brother, I argue that an intruder is someone who enters after the first eviction.
2012: Like previous series Benjamin, Ryan, Ray and George were all introduced in the first week like the others, they didn't intrude.
2013: Jade, Drew, Sugar sisters and Rohan all entered prior to nominations, thus are latecomers.
2014: Cat, Sam, Lawson and Aisha are the same as mentioned above, they entered on the second day.
2020: Chad, Sophie, Garth and Sarah whilst entered after an eviction had occurred, the first week was still going which in my mind is still a week of introductory. Hannah, Soobong, Danni and Shane also all entered within the first week.
2021: Same as 2020. The BB Air 8 all entered in the same way as the day 4 entrants in 2020.