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Thanks Dieter for your question. My development of TI (as PTI) is based on the Davies theory, a direct-action version of QED:
Davies, P. C. W. (1970). “A quantum theory of Wheeler-Feynman Electrodynamics,” Proc. Cam. Phil. Soc. 68, 751.
Davies, P. C. W. (1971).”Extension of Wheeler-Feynman Quantum Theory to the Relativistic Domain I. Scattering Processes,” J. Phys. A: Gen. Phys. 4, 836.
Davies, P. C. W. (1972).”Extension of Wheeler-Feynman Quantum Theory to the Relativistic Domain II. Emission Processes,” J. Phys. A: Gen. Phys. 5, 1025-1036.
Davies notes that the Feynman propagator can be decomposed into a time-symmetric part and a singular part. I identify the time-symmetric part as describing internal lines (virtual photons) and the singular part as external lines (real photons). Real photons (Fock states or offer waves in TI) prompt an absorber response (‘confirmation’) while the virtual photons do not. (It is the response from absorbers that transforms the time-symmetric propagator into the Feynman propagator.) This is discussed in http://arxiv.org/abs/1312.4007