Yasmim. kho, vaccha, samaye imañca ka’yam. nikkhipati,  satto  ca  aññataram. ka’yam. anupapanno hoti, tamaham. Tan.hu’pa’da’nam. vada’mi. Tan.ha’ hissa, vaccha, tasmim. samaye upa’da’nam. Hoti’”ti

SN 4.400  At that time, Vaccha, when a being has laid down this body, and that being (satto) has not yet taken up another (annataram) body (kayam) in rebirth (anupapanno); therein I declare [that beings] fuel to be thirstfulness (tanhupadanam). At that time, Vaccha, I declare [the beings] fuel to be thirstfulness.
 

Theravada redefines Buddhism to accord with its own anti-foundational views within the Milindapanha at:
Milinda #40 “Just so O king, is the continuity of a person or thing maintained. One comes into being, another passes away; and the rebirth is simultaneous.”
(Milinda is Abhidhammic literature and it not part of Orthodox Buddhism)
 

This simile of Samsaric ‘transmigration’ (found in Abhidhamma as well) is explained as “one flame to another” without gap or interim which is not the view of Nikayan (presectarian) Buddhism.
The admission by Theravada of an autonomous entity/being/citta which, after death, is in between khandic psycho-physical/corporeal involvement is altogether too much for Theravada to embrace since this is in full rejection of Theravada/Abhidhamma dogmatic nihilism which runs contrary to and opposite that of the Nikayas themselves.