My maiden surname was almost inevitably misspelt or mispronounced, and I can remember my father saying to me, probably in consequence of this, that spelling someone's name incorrectly was the height of rudeness. However, this is comparatively recent thinking, and in the past spelling simply wasn't that important, and the further back you go, the more surname spelling variants you are likely to find. I have come across differently spelt signatures within the same document.
Not making allowances for spelling variations and mistranscriptions when searching can very easily contribute to the kind of errors and wrong assumptions we see in some Ancestry trees. 'Absence of evidence is not evidence of absence' - or in other words, not finding someone in a search doesn't necessarily mean they are not there.
Sometimes we need to be pretty imaginative with our search terms (remember the old riddle about 'photi' or 'ghoti' being feasible phonetic spellings of 'fish'), other times some good old-fashioned browsing may be called for.