Officially the pony years 1982-1983 and 1983-1984 can be considered as seperate issue years, and it is difficult to apply a proper chronology. It's also hard because ponies came out in different countries at different times - nonetheless the dating provided on this site is meant as a rough framework to when ponies were released.
1983 essentially saw the beginning of variety in the My Little Pony line. There were the first Unicorns, Pegasus Ponies and the first gimmick - the Rainbow Ponies with their multicoloured hair. There was also the very first Baby Pony, and three pony playsets for the ponies to play in.
It's worth remembering, however, that information on the UK release at this time is scant and inconclusive. All that is known for sure is that several of this years' more interesting ponies - namely the storesold Baby Ember and the Unicorn and Pegasus ponies were not a part of the United Kingdom line.
Why that should be, only Hasbro knows - as it was, British children still got to meet many of these pony characters through the My Little Pony comic that began two years later, in 1985.