As the update currently stands only new shops will receive the new items as they are being built up. This is not an oversight or a bug, each shop should get two items for every trader level and so it's not as easy as simply adding items to existing shops.
We could always just randomly take away items to replace with set items but I guess players wouldn't like that either.
The developers are going to try and think of a solution but as it currently stands its not a bug.
Solution and Logic:
The way I expected it to happen would be:
Each shop (adhering to current level) would have a % chance of simply getting each new item (in addition to current items). This would mean that existing shops
could, indeed, have more items "than they should." But is there anything
fundamentally wrong with that?
As it stands now, the update has set a precedent -- that legacy towns are obsolete, and will only become more so as future updates are released. If anything, legacy towns should be rewarded for having entered the game in its early stages. For now, there are no such rewards for player loyalty to The West. That's a problem for me, especially when an update moves in the
other direction -- snubbing legacy players and their towns. I've spent a lot of money on premium bonuses, and a good deal of the resulting rewards have been dumped into my town.
So, obstinate "fairness" doesn't exactly cut it for me in this case. Why should a new player/town's progress offer more interesting possibilities than mine does/did, simply because I joined early and stuck with it? I would be interested to know if any other legacy players feel this way, too.