My 3g-grandparents James Hyland and Catherine Delaney of Queen's County, Ireland, left there for Oldbury, Worcestershire, England sometime between the birth of their daughter Mary Ann (my 2g-grandparent) in 1845 and her next younger sibling Catherine in 19 January 1847 in Oldbury. I know of 7 children for James and Catherine (the 3 oldest born in Ireland, the 4 youngest born in Oldbury). So I set about adding all these Hyland children to James and Catherine.
Nothing odd happened when I added the oldest child, Peter, but when I started to add the next child, John (born about 1841), up popped two possible matches in the FamilySearch Family Tree. One was born in 1843 and died in 1897, married Margerett Keely, and was the son of a James Hyland and a Catherine Delany. The other was born in 1845 in England, died in Newark, NJ in 1897, married Margeret Kaley, and was the son of James Hyland and Catherine Keely. I felt fairly certain that these were all the same person. So I set about merging all the duplicates that had not previously turned up. As I went through this process, even more duplicates turned up. By the time I was done merging all the various John Hyland clones, I had 6 different entries for a Margaret Keely (various spellings of Margaret and of Keeley)
And before I was going to merge all the duplicate Margarets, I went back to James and Catherine, now that 2 new duplicate couples had been found for them. One was definitely the same couple (even had 2 censuses attached which I had previously seen for my own James and Catherine). And even for the one I knew that was mine, someone had attached a source to James and Catherine that didn't seem to have any connection to them at all, so I detached that one.
The other James and Catherine had ended up in Cumberland, England, with their son John born in Scotland. So I set about detaching that set of parents from my John.
Once I had John figured out, I went back to all the entries for his wife Margaret. It took a while to merge all her duplicates, but I was able to do so.
What would I find tomorrow when I looked at all of the other siblings of Peter, John, and Mary Ann?