When it comes to determining whether a branch of the family tree diverged to follow the trail of a misleading name twin, one detail that can serve as a warning is location. In Franciszka Olejniczak's case, two records supposedly for my second great-grandmother provided different locations, one for the each of the events on record. One identified the town of her birth as Jezewo. The other showed her marriage in Jaratschewo.
If Polish tradition follows that of several other countries and a wedding was customarily held near the bride's home, we are in trouble if we assume each of these documents represented my second great-grandmother. While I certainly can't ask any of the wedding guests if the bride was the "real" Franciszka, digging deeper into information on the two towns might provide some guidance.
First step might be to see how closely the two towns were situated. Though this involves Polish ancestors, I know one piece of advice from researching my father-in-law's Irish ancestors was always to map out the distance between the two towns; if their locations were within a reasonable walking distance from each other, that might make sense.
However, these were names in German given to towns which were then part of Prussia. Maps today correspond to current geo-political boundaries. My first step, then, would be to consult an online version of Meyers Gazetteer. But to look for Jezewo, the town where Franciszka was baptized, I already run into problems: there were not one, but three places which went by that name. Which was the right one?
Checking all the details on that baptismal record, thankfully it provided not just the name of the family's home, but also the "Kreis" (district, similar to the American county) and the province. Returning to the Gazetteer, we can see that the third choice offered, Jezewo in Gostyn, matches the baptismal record. Thankfully.
From that point, I turn to Google to search for the modern-day name for the Polish town once called Jezewo in Prussia. The transformation was barely perceptible, with one tiny diacritical mark added for the benefit of pronunciation: Jeżewo. Once I added the second destination on my map, the location of Franciszka's marriage, I determined that the 7.4 kilometer distance between the two was reasonable enough for a possible move for the family, or a marriage celebration in a nearby town.
In going through these steps, I also explored what else could be found on the two locations, both historically and through genealogical sources. It's always handy to stumble upon helpful other resources, and this search led me to some I'll be bookmarking.
One helpful resource I found in this process was an inventory of available church records for the Prussian province of Posen. This useful table includes a large listing of records from the FamilySearch catalog, searchable by locality, Kreis (district), and church organization. Each entry under the heading "Title" is clickable and leads to that line item's record set. For instance, clicking on the entry for Jeżewo brings me to church records in multiple image group numbers for that village alone.
Record sets like those included in this finding aid at FamilySearch.org will keep me busy working my way through the many Olejniczak descendants I've managed to add to my family tree so far, providing another resource to compare with what I've already been able to find through the Polish online resource BaSIA. The process may be tedious, but it is allowing me to work my way from the early 1800s with Franciszka's parents, well into the early decades of the 1900s. Hopefully at some point soon, I'll have enough information to dovetail into the family trees of my Polish DNA matches.