My thanks to all who have responded, and please forgive me if I do not answer the individual posts - the result would be too fragmented.
Maybe I failed to put the problem clearly: of course, there have always been spelling variations and plain mistakes. If there is a single example of a "Lidlaw" in a period of 300 years, then to assume that this is a variation of Laidlaw is easy, and one can proceed without much risk of propagating an error.
But names do vary over time, with the result that some variants become established as names in their own right. A fellow student always gave his name as "Clark with an e" (i.e. Clarke). Once upon a time "Clarke" may have simply been an alternative to "Clark", but if we were now to relabel the 21 thousand Clarkes on WikiTree as Clarks (because that is the "standard form", with 73 thousand entries), the result would be chaos, not clarity.
In other words, there is a point at which correction becomes falsification, and I was hoping that someone could give me a guide as to where that point lies.
In my own case, I have established to my own satisfaction that "Laidla" came about as a variation of Laidlaw in the parish of Hawick, being amost entirely local and disappearing about 1730. The detailed demonstration is too involved to be presented here, and I'm not even sure if it would be of general interest.
The question - to which there is no simple answer - is "When does correction become falsification?"