Action in Conversations happen right at the very beginning, so if you have a variable as a flag for a topic it will be true right away.
I just realised i can use Alt descriptions for this.
Also as an additional suggestion, restrictions for (conversation restrictions and ordinary tasks) could have 'Conversation' restrictions much in the same way as checking if task has completed or not. eg. If Conversation - Topic Name - has completed. This would save having to use variable flags.