The purpose of the on-screen "Correct Display" button, new in Aleph version 16, was a bit obscure to me, but now I think I understand it.
In v14, Aleph was hypersensitive to small differences in the display form of its headings, to the point that minor differences in capitalization or punctuation could split a heading into two entries. In v16, this sensitivity is reduced, which is good on the whole and relieves us of lots of work to merge split headings. But a consequence of this reduction in sensitivity has been a break in the link between the heading form on the record and the display form in the index entry as regards these minor differences. This comes through most clearly when one is correcting a minor discrepancy in a single entry, for example:
"Biology--Polar Regions" should be "Biology--Polar regions."
There is only one hit for this heading. The Correct Heading button lets me change the bib heading to "regions", but the display form of the heading is not changed--it still shows "Regions." To complete the correction, I use the Correct Display button. It lets me doctor the display text in the index record to the form I want. Having taught Aleph not to regard differences like R/r as significant enough to result in a separate display, we also have to accept that when we make such a change, Aleph will ignore it unless we intervene with the Correct Display button.
So my guess is that we'll use the Correct Display button mainly to tidy up the index after using the Correct Heading button to correct the bib data. If we used only the Correct Display button, the entry would look OK, but the underlying bib data would be uncorrected.
Please note that only a few staff are authorized to use the Correct Heading and Correct Display buttons. If you have corrections which would best be done with these buttons, please report them to firstname.lastname@example.org