Hmm, interesting theory but highly unlikely. For those that dont know or have forgot my dad used to make the molds that are used to create plastic parts. His job is the person who makes the actual mold so i know quite a but about the process and its highly unlikely the 2 molds are unintentionally different. When the engineers and designers create a design they then use specific computer programs (CAD or AUTOCAD) to design it and see it in 3-D, then the program is used with conjunction with another program to create the designs for the mold. After that a human engineer goes thru the entire computer generated plan and checks everything to ensure its all correct. After that a person puts the program into the computer on the machine that makes the initial mold. After that another person takes the paper generated mold idea and compares it to the rough mold to ensure it is correct. From there another person finishes the molds internal aspects and checks it again for correctness. After that the mold goes to a polisher who makes the metal smooth so the plastic is smooth who again checks the pattern. Before it ever leaves the shop several test runs are made and shipped to the engineers to look over and see if they want to change anything. After all engineers determine they like the finished product the mold is shipped to the company.
Unless cosco wanted molds of different height they would have ordered 2 molds made of the same computer plan since the cost of engineering the mold plan and inputting it into the machines is not cheap. Even if the inputer made a mistake inputting the code into the machine it wouldnt affect it like it appears to, it would have garbled the entire code and messed it all up.
I've seen all of the apex patterns (i think. blue, red and brown right?) and there is defiantly a padding difference but I've never found a considerable difference in top slot height. Are your friends the same model and cover? Thats really strange, maybe the child isnt sitting properly is one?