Ikea Maxima drawers do not fit??

A friend received an Ikea kitchen. Now she wanted a different "interior" for the 40 cm carcass, namely instead of 2 large drawers the version with 3 drawers, so that she also has a cutlery drawer. We picked it up yesterday and I was able to assemble the three drawers, but not install them in the carcass, as we had to leave. Now she is doing it today with a friend (both have no idea about Ikea assembly), and the following problem occurred: The three fronts apparently do not fit together. I tried to explain to her that this is certainly not an Ikea error and the interior fittings are standardized, and that a) it is either an error from yesterday during drawer assembly (I exclude this, since it is actually specified where to screw what) or b) they made a mistake assembling the rails. What could be the reason? The bottom drawer does not go down any further, and there is only one way to mount the front. Could it be that the rails for the 40 cm drawer are different from those for the 20 cm, and a rail for a 20 cm drawer was installed at the bottom?