What it means is that the range of carbon for that steel is from .75 to .80 . Whatever the carbon content ( within that range) ,the manganese and other trace elements will be the same. For practical purposes, this steel is the same as most 1084. Most steels vary about .05% from batch to batch. What Admiral is saying is that they don't individually label each bar as to what the exact content is.
Aldo's 1084FG has vanadium added to refine the grain size, and extra manganese to deepen the hardening. This makes the steel forge better and HT easier.
Whether from Admiral or Aldo. steels in the range from 1075-1085 are great starter steels.