What it is saying I believe is that by 84 in the USA and 85-UK the 1.8 GTI engine became the standard power plant for the "GTI" Cabby models, which succeeded the Gli.
It's not saying that models prior could not be a GTI, there were a lot of quick changes engine wise over a few short years, you had the GLi etc beforehand which still had an injected engine albeit a 1.6. A 1.8 GTI engine was available as early as 82 for the GLi. So you could get both models with a 1.8 GTI engine.