Thank goodness for the Other Last Names field. As you noted I try to get the LNAB as found on a birth or christening record; though, when finding six different records on a person 3 different spellings are not uncommon. The further back we go, the more we see this as those that could write often used phonetic spellings. Another reason I've found is when dealing with church or parish records where those who documented names tried to assimilate all Wilson, Welson and Willson names the same, Burton, Bertan, Birtun names the same, Willet, Willit, Willits, the same, etc. IOW: when searching we need to keep in mind typical variants and sometimes a bit of imagination is required as we look for documents that contain multiple members of the same family.
Helmut, you say, "There one has to follow established practice."
What is the established practice? Thank you :-)
Not necessarily, see:
Unfortunately, the only way to be sure are documents showing what form of the name was used.