Your first bowl is indeed Three Fruits Medallion by Northwood. It is marigold and is stippled (which is nice) and it has spatula feet. The exterior pattern is Meander.
The second bowl is currently a puzzle. I have encountered it twice and both of the other examples are also from Australia. It has many of the characteristics of Imperial's glass but yet it is not one of their known patterns. It could be a European pattern but again, it's not something I have so far been able to ID (perhaps someone else may be able to help).
Your third bowl is not Australian, but is in fact Imperial (USA) and the pattern is Oval & Round.
You ask how to tell new from old Carnival? It's not easy. Sometimes there is a trademark which will help, sometimes the iridescence or the specific pattern or colour will give clues, or you simply have to read, read, read and experience the joys of Carnival collecting.
Glen