If you're not using FTAnalyzer then you need to give it a go, it will help you find who can be added to Lost Cousins, and a whole host of other data reports, unlocking the data that your hold in your Family Trees.
The new version 3.5.0.0 which will be out at the weekend includes a new feature to display all the people in your tree that has census facts stored as notes. This should hopefully help those individuals whose family tree program has erroneously stored census data as a note rather than as a census fact.
Researching the issue it appears that early versions of some programs didn't have census facts as a type of fact you could add or they thought users would be lazy and not bother adding census records to each person on the census. So they got round the problem by cutting and pasting the data from a census into a note. Unfortunately this doesn't adhere to the GEDCOM standard and means if your program did this then the individuals in your tree may not have a proper census record just a bunch of text in often fairly random format that is a census entry.
The downside of having your census records like this is that it is so much harder for you to see who is missing from a census as you have to read each note to check, sometimes you even have to read the notes of a parent to see if a child was on the census. The idea of this new report is to highlight to people how many of these partially hidden census entries they have. Shedding a light on these then will aid users should they wish to update their tree to actually record the census fact as a proper fact against each individual.
Having proper census facts means it is very much easier to see at a glance in your family tree program and indeed in the census reports in FTAnalyzer who is missing from a census which can be a spur to making new enquiries and finding leads that break down brick walls. Seeing clearly where there are holes in your research is a great way to make new discoveries, by filling those holes.