This thread might be useful: Stillness and liberating insight
I think there is some confusion about the amount of samadhi required- it seems to me that a degree of samadhi above the first jhana is essential for nibbana. After entering that territory getting off of at any of the stops along that train line, you are still going to nibbana (in the land of nibbana, if you like), having crossed the border, of the first jhana samadhi.
These jhana states are called ‘temporary nibbana’. However this is not to say that everyone who attained jhana (ie those recluse before and in other religions at the time of the Budha who attained jhana) were entering nibbana, as the insight element was absent in those other teachings and it would have lead to heavenly planes of existence, rather than nibbana ‘proper’.
with metta