This is another serious issue.
In almost every case, the actual buds entered into a contest represent the absolute best pheno of the line, grown by experts with many cycles of experience dialing it in perfectly, harvesting at its peak. In other words, you're getting the absolute max potential of the line entered into the contest. You may not ever see that cup winning pheno in your particular pack of beans, and even if you did, you probably aren't going to max its potential the first time you grow it.
In at least some cases, the genetics entered into the contest isn't identical to the genetics in the packs.
Also, over time, parent plants get lost, stuff gets diluted out by multiple generations of crosses, or the original breeder just reworks the line for other reasons.
If you look at the commercial market now, not only are there 10 different things called "Northern lights" and "White widow", they're all different from each other. Not even getting into which of these are or aren't good, obviously, these all can't be cup winning genetics! With certain cup winning lines (eg AK-47 and Kali Mist, to name two), the breeder has changed the genetics since the cups have been won.