I often hear the same problem about genealogical research. It is the inability to find an individual or family in a certain record. Most commonly, this complaint is that the ancestors cannot be located in one or more of the U.S. Census years. Although it is entirely possible that a family or, more likely, an individual was overlooked by the Census enumerators, my experience is that a more exhaustive search of the record often turns up the "missing" reference. I call this approach to finding records the bulldozer approach.
Essentially, bulldozing the records involves a line by line search of an entire record source. I have done this many times with census records and many other types of records, such as parish registers, town records, probate files, and similar types of records. In each case, as a researcher, you would expect that the record contains some reference to your family, but you find no mention in any index or extractions. The only way you can be sure that the records do not exist is to go through the source line by line and page by page.
Most of us who started back in the "old days" of microfilm, are very familiar with bulldozing because we had no other way to find pertinent records. I fear that today's instant gratification society may have soured most of the researchers on the down and dirty work necessary to find some types of records. I know people who stop after only one or two pages, thinking that if the record hasn't shown up with a brief search, then further searching is futile. There is no solution other than to finish the job, search the entire record available and re-search it if you still don't feel comfortable that your ancestors were not in the record. Sometimes, it has gotten so bad for me, that I have to shut my eyes when re-winding the microfilm in order to avoid getting motion sickness.
Another aspect of bulldozing is to go to a major library, such as the Family History Library in Salt Lake City, Utah and spend time looking at every single publication for a particular state. For example, I have individually looked at every single publication, book and pamphlet for the state of Rhode Island looking for information about my Tanner ancestors. There is really no other method of having the assurance that you haven't overlooked something important.
When was the last time you looked at every database for a specific jurisdiction on FamilySearch.org or Ancestry.com? Did you expand your search to every other resource you could find online and at the other repositories? If not, you need to hire yourself a bulldozer and go to work.
Some of the benefits of bulldozing are not always immediately evident. As you systematically work through piles of old records, you begin to learn what is and what is not available in any given type of record. Your expectations become more reasonable and you get a perspective on the types of records that you might find in other contexts. For example, in reading the old Rhode Island town records, I discovered that the Town Clerks recorded the cattle brands for the community and was able to find my relatives cattle brands, something I had not imagined existing before I bulldozed through the records.