  We argue that the modification proposed by Li et al. [Chin. Phys. Lett. 32,
050303 (2015)] to the experiment of Danan et al. [Phys. Rev. Lett. 111, 240402
(2013)] does not test the past of the photon as characterised by local weak
traces. Instead of answering the questions: (i) Were the photons in A? (ii)
Were the photons in B? (iii) Were the photons in C? the proposed experiment
measures a degenerate operator answering the questions: (i) Were the photons in
A? (ii) Were the photons in B and C together? A negative answer to the last
question does not tell us if photons were present in B or C. A simple variation
of the modified experiment does provide good evidence for the past of the
photon in agreement with the results Danan et al. obtained.
