OK, I expect that when I use WikiTree name search to search for a name, the algorithm will look for the last name in all of the last name fields (LNAB, Current Last Name, and Other Last Names), and it will treat multi-word names like Van Steenwyck the same as if they were spelled as one word (such as Vansteenwyck).
Another member pointed out that the profile linked in the question will not turn up in a search for "Altje VanSteenwyck" (nor "Altje Vansteenwyck") although her first name of Altje and the "Other Last Name" of "van Steenwyck" have been in the data fields for at least the past 1-1/2 years (that is, these are not new entries). I did find that this profile will appear in a search if I use a wildcard character and search on "Altje *steenwyck", but not in any combination that includes both "van" and "steenwyck."
I've tried a variety of other search combinations to see if I could find the pattern of parameters that cause the name search process to fail. It works fine with one-word last names that appear only in the Other Last Names field (if I search for "Deborah Champion", https://www.wikitree.com/wiki/Palmer-1650 is one of the results I see) and most of the time it works for two-and-three-word last names (whether they start with a lower-case letter or an upper-case letter) in the Other Last Names field, but I've found that it fails when the multi-word name in Other Last Names is not a recognized variant for either the LNAB or the Current Last Name. Thus, if I search for any version of "Altje Van Steenwyck" (other than that wildcard search) I don't get Altje Albers because neither of her primary last-name fields looks anything like Van Steenwyck, and if I search for "Wouter Van Wythorst" the results don't include Wouter Albertsz van den Uythof (because Van Wythorst is on that profile as an Other Last Name and it has no apparent relationship to either Albertsz or van den Uythof).
Can this behavior be fixed?
