Hermann goes even further: complete forms (e.g. *deiwos) cannot be reconstructed at all, only single sounds, and even these are meant as approximations only, not as phonetically completely correct reconstructions.

Quoted from Kazanas, N. (2009). Indo-Aryan origins and other Vedic issues. Chapter 9 | Eduard Hermann | Szemerényi O. 1996 Introduction to Indo-European Linguistics (translated from German 1990, with additional notes and references) Oxford, OUP. page 33.