This doesn't answer your question, but I would like to mention something that I am currently researching. My great-aunts were recorded as twin births in Szrensk, Poland in 1910. Living relatives who knew them are adamant that they were not twins but merely sisters born 2 or 3 years apart. I am trying to figure out if there was a logical explanation for recording siblings' births as twins - maybe no possibility of recording births at the actual time, maybe some sort of reason as to avoid taxes or the draft, but none are logical explanations so far.
In our case confounding the mystery, these great-aunts' grandmother was recorded to be a twin (whose birth was actually recorded 3 years after the birth!) and there are other twins in the historical family, so twins doesn't seem to be out of the question.... unless all those other twin births were not really twins either!!!