Actuall, I have learned that the N14121 ID was indeed actually used for many years. I posted a general info notice to Zane Adams especially, and anyone else. The 557 c/n is a mystery. I've done a lot of research and Mike Henninger at Aerial Visuals took my lead and did more.
The FAA says the plane was built in 1993, which would have to be a rebuild. The plane was originally a T-28A built ca. 1952, and then, if I recall without going to A-V, in 1960 was sent to France where it was converted to A Fennec version. After they retired it the plane came back to the USA where it was converted to T-28D standards for Haiti, and when they retired it, the plane again came back to the USA. Spent about six months with a Canadian registry. Spent some time flying air races.
Perhaps whatever took place in 1993 - conversion or total rebuild - gave rise to a different c/n? Or perhaps that happened in the conversion to T-28D for Haiti?
Perhaps you'd find it of interest to look at the dossier Mike and I built over at Aerial Visuals:
http://www.aerialvisuals.ca/AirframeDossier.php?Serial=26316