I often wondered after the Intellivision started to sell well if they integrated it into Mattel proper. Like maybe some folks at Mattel did not give it much chance of success so they started out with actual off the line numbers..
Then when it became a sucess they added it it to the other Mattel product line codes. It seems those numbers started to get higher quicker.
It might have been a way to track the Intellivsion better with in the company. If at first it failed they might have thought well we only sold x amount.
Just a thought! Hope it makes sense and others can expand on this?