Well, my little fun exercise chasing John Moncur through Napoleonic era naval lists and so on has shown me that it’s perfectly possible to use open source materials, with two important caveats – firstly, the person investigated has to be a ‘person of quality’ (Jane Eyre would know what is meant here), ie someone who appears in the army or navy lists, or local almanacs which include lists of electors from the days when only property owners could vote.
Women are invisible, or they are at least until 1811 with the first census, and the same goes for ordinary people including tradesmen and small farmers who did not meet the property qualification.
The second major requirement is that the documents need to have been digitised and OCR’d to render them searchable. Thanks to the Google Books project, a lot of them are, and the OCR conversion of the scans is of sufficiently high quality to ensure that the text is more or less searchable.
As well as these two requirements. having a slightly unusual name that is sufficiently unique to make searching reasonably straightforward definitely speeds the process …