Actually Buddhism was propogated by everybody other than Buddha himself. He just taught Dhamma which is universal, a universal remidy for a universal suffering. Please give me just one quote from entire Tipitika where where Buddhism / 'bauddha' as a word is mentioned. You will not find even one mention. And as per Buddha's own words from aeons perhaps India has been a country of Buddha's / Pacceka buddha's and those words keep filtering down. You practise Vipassana and suddenly find that words of various mystics have a very differnt meaning.
I for one am just a follower of Vipassana , along with Buddha's / other wise people's words; wherever that takes me. Rest does not matter.
Your / others futile effort in trying to define Nibbana will and cannot take you even an inch closer to defining it literally / figuratively / any other 'ly'. The point I make is "the unconditioned can't be defined". Better to invest time in the practise and work on.