SuttaCentral
I was reading this translation of a Chinese sutra, by Bhikkhu Khantipalo, published by the BPS.
According to the document, it corresponds to Volume 12, Number 389 of the Taisho edition (or Number 122 of the Nañjio Catalogue of the Chinese Tripitaka).
I tried to locate it in SC but could not find it. Is this the original sutta on SC?
What a beautiful discourse this one is! 
A lovely text, thanks for sharing.
However, it doesn’t appear on SC, being a later text not regarded as part of the EBTs. No doubt many of the passages in this text could be regarded as parallels to EBT passages, but our parallels do not, unfortunately, cover such cases.
As to the numbering, the T (= Taisho) numbers can be confusing. The Taisho canon is referenced both as vol/page of the printed edition, and by “sutra” number, where “sutra” in this context means any text collected under one heading in the Taisho edition. For example, the Dirghagama is one “sutra”, as is, say, a Vinaya. But an individual sutra such as this one may also be considered as “sutra”. I said it was confusing!
But the main point is that the sutras are numbered by simple sequence from the start of the collection, not per volume. Thus the sutra reference alone is sufficient to locate the text.
On SC, t-numbers refer to the sutra number. So T 12, which you refer to, is Taisho sutra number 12, which included in Volume i, and which happens to be a parallel of DN 33. So no, that’s not what we’re looking for.
This parinirvana style text would be referenced on SC as T 389. The original Chinese text may be found on CBETA:
Thanks a lot for the explanations about the Taisho numbering, very helpful.