[dodgytrousers]

The beckett database states this:

"Released in February 2004, Genuine Insider features a 140-card set divided up into 100 veteran player cards, 10 rookie cards sequentially numbered to 499 (cards 101-110), 20 rookie cards sequentially numbered to 799 (cards 111-130), and 10 mini rookie cards sequentially numbered to 350 (cards 131-140). The mini cards are found as inserts inside cards 101-110, hence the product name, Insider. Base cards feature colored background with the main focus being color to match the player's team colors. Genuine Insider was packaged in 24-pack boxes where packs contained five cards and carried a suggested retail price of $4.99."

The mini cards were inserted randomly so they were not always the same player as the main card.