I don't know but what I am aware of, is that the INC founder Felix Manalo have received the office of being a Pastor and as a "Tagapamahala ng Iglesia" on December 25, 1918. The 5th anniversary of Iglesia Ni Kristo on December 25, 1918 confirms that INC indeed, started in 1913 and not 1914. This is also a clear and logical argument that INC may have started as a "church" in December 25, 1913 since the Pasugo (July 27, 1989) stated that the first fruits of his preaching were baptized at the Pasig River in late 1913.
If the Iglesia Ni Cristo celebrates the January 1 New Years Day, I think it would be acceptable (for INC) to also celebrate the INC anniversary during December 25, as Felix Manalo have previously celebrated also.
Iglesia ni Kristo
Maynila, Disyembre, 1918
BUHAY AT KAPAYAPAAN
Mapitagan naming inaanyayahan ang iyong kamahalan sa gaganaping pagdiriwang ukol sa PAGPAPASALAMAT sanhi sa ika LIMANG TAONG BUHAY ng "IGLESIA NI KRISTO" sa Pilipinas at PAGPAPATONG NG KAMAY sa kapatid na Felix Manalo sa tungkuling pagka Pastor at Tagapamahala ng Iglesia. Ito'y idaraos sa Sine "Gloria" blg. 1649 daang Sande, Tundo, (Maynila) sa ika 25 ng Disyembre sa taong ito sa ganap na ika walo ng umaga (8:00 a.m.) ng nasabing araw.
Lubos ng aming pag-asa na pararangalan ng inyong pagharap ang nabanggit na pagdiriwang sa araw at oras na nabanggit.
Ang mga gumagalang,
Pang. ng Lupon
Kalihim ng Lupon
Kagawad ng Lupon
THE BARRIO OF Punta, Sta. Ana lies at the confluence of the Pasig and San Juan Rivers. In this place, Brother Felix Y. Manalo began fulfilling the prophecies of God about His last messenger who will emerge in the Far East at the time called "ends of the earth." He first introduced the Church to the workers of Atlantic Gulf and Pacific Company (A.G. & P.). The first fruits of his preaching were baptized at the Pasig River in late 1913..
Pasugo - July 27, 1989