Our search system only searches for words the way you spelt it. But the spelling in the different sources can vary widely from the modern way of spelling, as well as from the way the person in question normally spelt his/her name.
In order to find what you are looking for, you can use a wildcard, e.g. an asterisk* before or after that section of the word you are certain of. *sto* will find all the above-mentioned versions of the name Kristoffer. Read more about these possibilities under the different headings in the menu to the left.