Giles Plantz was married to Etta Plantz and had a daughter named Nina -- that much was clear from the census. Other people had trees indicating a marriage date for Giles and Etta both before an after Nina's birth. On the one hand, the marriage date before Nina's birth made sense. On the other hand, it didn't look like a simple transcription error and the trees in question were relatively accurate.
Google books to the rescue! From _History of Montgomery County: Embracing Early Discoveries, the Advance of Civilization, the Labors and Triumphs of Sir William Johnson, the INception and Development of Manufactures, with Town and Local Records, Also Military Achievements of Montgomery Patriots_, p 104:
"Plantz, Giles H., Amsterdam, Fort Johnson p. o., was born in Perth, June 19, 1845, and is a son of Michael and Charlotte (Plantz) Plantz. As far back as our subject can trace, the ancestry were natives of this country. Peter Plantz, grandfather on the mother's side, was born about 1790 and died in 1875. He was the father of ten children, Charlotte being one of the number. Michael Plantz, and grandfather on the father's side, was born about 1785 and died in 1870. He was the father of five children, of which Michael, the father of our subject, was next to the oldest. He married Charlotte Plantz, and they are the parents of six children, four now living: David of Perth, Elizabeth, now Mrs. John H. Putnam of Johnstown; Melissa, now Mrs. George Joslyn of Perth; and Giles, our subject. He was educated in the common schools of Amsterdam and always lived there until his marriage, December 28, 1870, to Etta Hough of the town of Mohawk, and they have one child, Lottie E., born August 20, 1875. Mrs. Plantz died the same day. After his marriage he moved to his present residence, a fine farm of 143 acres. February 20, 1878, he married Etta Putnam, daughter of Aaron and Sarah A. (Hubbs) Putnam of Johnstown. Mr. Plantz has always been a successful farmer, diligent and industrious. He has never been a political office holder, but devotes his whole time and attention to his business."
I harbor a suspicion that Aaron, Sarah and Etta are not Putnam but rather Putman but I'm still looking for something definitive. But there are certainly two wives named "Etta" for Giles Plantz.
[ETA: Definitely Putman. However, even people doing transcriptions in Johnstown Cemetary are not getting it consistently right -- even within a family plot. It's _really_ frustrating.]