Even though Hornby do change their release dates without telling the retailers, at least they do update the dates on their system so that the retailers can find the information.
For a lot of the ranges, the release date comes and goes and nothing appears, sometimes for months without any update from the manufacturers.
Then there are the companies that will announce kits that are 'coming soon' in the magazines, but they don't appear for years is at all.
Then throw in the companies who's items become unavailable without warning, while still being on their listings, with no restock dates. These kits can go out of stock for months, even over a year in some cases, then suddenly turn up without any indication that they were on the way.
There are also companies that only release final details of their kits when they are released, including the price, making it impossible to advertise them ahead of release and take pre-orders.