Jetting questions on a '91 250x

I got around to rebuilding the carb last night. The dealer told me that I need a 119 main jet. Nothing about the slow jet. My kit came with a 122 main and 35 slow, and the quad has a 125 main and a 38 slow already on it. For what reason would the previous owner have put a bigger jet in when our altitude says to go lower (I bought it locally from a guy who had owned it for 10 years)? How big of a deal is the slow jet because the one that came with the lit won't work. It's too long and it gets in the way of the bowl so I put the original 38 back in.