The parole status of the Jaffa prisoners has never been proved. It is a feeble excuse for massacring men who have surrendered.
In looking at the references, I did wonder how the former garrison of 'El A'rych' - as described in 'Commentaires de Napoléon' (1867), were identified as such after the fall of the city, having been diverted to Jaffa, while en route to Baghdad as per terms of their parole. I doubt they would have volunteered the fact.
Were regimental distinctions a feature of Ottoman military dress at that date? Apparently those executed were troops of Albanian origin. Was it their Slav-Greek features that gave them away? Ottoman troops were in general a heterogenous mix.
The description of their fate is somewhat understated.
'Il se trouva 2,5oo prisonniers, dont 8 à 900 hommes de
la garnison d'El-A'rych. Ces derniers, après avoir juré de ne
pas rentrer en Syrie avant une année, avaient fait trois journées
dans la direction de Bagdad, mais depuis, par un crochet,
s'étaient jetés dans Jaffa. Ils avaient ainsi violé leur serment :
ils furent passés par les armes. ' (Vol III. p.44)