when i played this game years ago, i scratched my head on this one too.

in real life, if i buy two items in the same category, i get to keep both. this artificial limit in the game seemed wrong.

i dabble in programming. if i had to guess, my guess is the limit was not done as a punishment or to limit the player. it takes a lot to write a game, and often things are set up quickly just to get the game working. in this case it was easiest to just make 4 slots and have each slot hold some category of product. i think the plan was that if time permitted after the working version was up and running, a new system of slots could have been implemented with an unlimited number of slots, and arrow buttons to scroll through the products. but there are deadlines to meet. i've found that there is always one more bell or whistle that would be nice, but if programmers did not release products until every bell and whistle was incorporated, we would still be using the DOS operating system, writing our letters in wordstar, and the shelves of stores like gamestop would be mostly empty.