The serology assay used in Lombardi et al. could never have detected an erv.

There are 16 human endogenous retroviruses (erv's) capable of producing a full length env protein.

Three are naturally expressed in PBMCs.  They are HERV-K  HERV-R and HERV-FRD. None are latent or methylated.

Only HERV-FRD is related to gammaretroviruses. HERV-FRD is better known as syncytin 2.

Hence only HERV-FRD would have been a candidate for reacting with the monoclonal antibody to SFFV env in figure C in Lombardi et al.

HERV-FRD would have produced an antibody response whether 5-AZA had been added or not.

The molecular weight of the FRD env is known and does not correspond to the molecular weight of the env protein detected in the patients in lombardi et al.

Thus the speculation that the culture of PBMCs activated by AZA could have activated a latent erv is not justified and is not supported by any scientific observations or other scientific evidence.