I think the significance is that she previously said that she had a good memory for names and that's how she searched the parents, often months/years later ( rather than using the handover sheets for that purpose).I don't really get the significance of this; if you search someone on FB and don't get the name exactly right it'll give you suggestions. As soon as you click on a suggestion to view the profile it records that profile in your search history, correct name and all.
You don't need to type the name correctly in order for it to be on your search history.
It's irrelevant whether Facebook offers suggestions even if misspelled, because Johnson will have the details of what spelling she used to search the parents. So if she used the (correct) spelling that was on the handover sheet to search them, and now in court gives a different spelling to that, it implies that she used the handover sheet to conduct her searches, and that without the handover sheet she wouldn't have been able to spell it correctly. The jury can then decide whether that sounds likely or not.