There are a number of reasons why something like this happens.
We have different sale agreements with different training companies, some of which allow us to put their courses on sale earlier than the majority but sometimes only authorize us having a small window for discount seating.
Some companies have early bird registration sales so advertise a discount to fill seats early. This is a feature not all training providers subscribe to and therefore you would still see most options not yet on sale.
Sometimes a training company needs to fill a large number of seats in a specific class/date and therefore gives us the authorization to discount a course sooner and/or lower than what is normally advertised for that particular class.