Retired in ISO 639-3: Merged into language element [opa] Okpamheri
Excerpt from change request document:
The change I am proposing is that Ibilo [ibi] be changed from being a language within [Edo- Esan-Ora, North Central, Edoid, Benue-Congo, Volta-Congo, Atlantic-Congo, Niger-Congo], and be moved to being a dialect of Okpamheri [opa], located within the Northwestern Edoid branch.
I have found no publication which places Ibilo within this subclassification. Nor have I found any dialect called "Ibilo" in these languages. In talking to Prof. Ron Schaefer (Southern Illinois University Edwardsville), who has extensive first hand experience with Emai and other Edoid languages, he knows of no languages or dialects called Ibilo in North Central. He also says that Ibillo is the principal village in the Okpamheri cluster, which include about 20 or so villages.
Further, Ben Elugbe (University of Ibadan) has written extensively on comparitive Edoid.
Elugbe (1989a: 24) cites that he used the Ibilo dialect of Okpamheri in his comparative work, and Elugbe (1989b: 296) notes that the Ibilo dialect is spoken in Ibilo town, and is a dialect of Okpamheri. He further provides in (1989b: 296) the consonant inventory of Ibilo, showing it has breathy voiced consonants, and a lenis/nonlenis distinction. These are features of the Northwest branch. The Edo-Esan-Ora language group of North Central, within which Ibilo is classified by Ethnologue, do not contain these phonological features.
Also, your map 6 of Nigeria (found at http://www.ethnologue.com/show_map.asp?name=NG&seq=80) shows that the code for Ibilo on the map is 305. This places it in the Northwest area of Edoid languages, not the North Central.
Finally, in a non-linguistics article, Oseni (1991: 224) notes Okpamheri people from a town "Ibillo".
These facts, I feel, warrant that its status as an independent language, with its own language code, be removed, unless there is some distinct evidence to classify it as a separate language from Okpamheri [opa].
There is the possiblity that evidence and documentation exists that Ibilo is its own language within the North Central branch, or that perhaps it is some dialect of a North Central branch language, which happens to be homophonous with a dialect of Okpamheri in the Northwest branch. If this is the case, I would be very interested to see which sources this information comes from.