If you are looking for exact dates - then there is a good possibility you will never find many of them. Additional research and common sense can help create reasonable estimates until a record (if one exists) can be found.
As far as spellings, I would suggest the only 'correct' spelling is the one the person chose to use - if they could write...
I don't think there has ever been a genealogist, amateur or professional, that has not struggled with choosing one of a dozen recorded spellings to use for an individual or family, or with discrepancies of dates and places.
Hopefully this is not telling you how to suck eggs, but In my opinion the best strategy is to research groups and not individuals. To reuse an example I have given before, in my research I could not find a particular family in a particular census under any of the alternate spellings that made sense - but I knew from other records what families they intermarried with, were neighbours with, went to church with and by expanding my net to look for this micro-community I was able to find the missing family who had been enumerated that year as 'Groulx' instead of 'Sproul'.