How nice of you to drop in. Life becomes more interesting when we find our name scattered worldwide.
I know that I have stated this many times on different sites, but it seems to me that all Gilsenans have their roots in Co. Meath. There is a preponderance of the name in this area, and surrounding counties to a lesser extent. I would love to know the reason, but I can't help but think that we are all branches of the same tree.
As regards the spelling. Existing "versions" of a name are often the consequence of somebody having made a mistake at Birth or Marriage registrations or such like. Here in Ireland my sister's name was incorrectly registered as "Gelsinan", and it has been more convenient for her to retain the incorrect documentation rather than go to the trouble of trying to alter everything. She has travelled a lot, so is aware of the many circumstances she encounters where she has to sign her name incorrectly in order to receive "clearance".I imagine that the other variants were created accidentally also.
Another common denominator to the "family" is an artistic thread that keeps cropping up especially in the fields of Painting, and Singing. and things generally musical.
Kind regards and Happy New Year to all Gilsenans/Gilshennans etc.