As far as the Antiochian WR Vicariate is concerned, there is no question that their liturgies and existence as a whole is legitimate: it can be proven by written evidence (WR decree, letter from the Patriarch, directory etc.).
But are you sure that this is the case for the ROCOR WR Community?
Is there any written testimonial, except the synodal decision of July 13th 2013 and the epistle from the Met. which followed some weeks later?
One often reads, i.e. that this or that liturgy or customed is "authorized" oder blessed for use (by whom..the First Hierarch? The Synod?) as stated on websites.
I have never seen any record concerning liturgical issues, and probably the ROCOR responsibles remain that way on the secure path, because if they formally would approve a WR liturgy it would be illegal, if not done by the Holy Synod in Moscow (according to the Statutes of the Russian Orthodox Church from 2013 V, 28, c).
The assumption that the WR is legitimate relies on the belief that a Bishop or the Synod of an autonomous church is the holder of the Jus Liturgicum, but his is not the case in ROC.
Therefor there is not only no concept behind it, the ROCOR WR seems to habe no legitimacy in current Russian Orthodoxy, it is just tolerated.
I would very much appreciate, if someone can refute my thesis.
BTW The Antiochian Ordo for Baptism mentions the use of oil of the Catechumens, but who blesses it (and the oil of the sick) and when? They dont have a bishop practising the WR, right? Just overseeing and without a Bishop all WR efforts remain uncomplete.