Considering that the term 'Generation 1' (or Gen1, G1) was only coined by collectors after 'G2' started, so it really refers to anything prior to 'G2' for fans to distinguish between the two (because a number of G1 toys were released in G2).
G1.5 was also coined later to refer to the issue dirge raised, in that the European originated toys had blurred boundaries. So anything of that period that originated from UK Hasbro instead of US Hasbro or Takara, is referred to as G1.5, or EURO as I call them (which doesn't meant they were only in Europe, but because that's where they originated).