The "Legend" is the "box" found on both the "page" created by eeSchema and the "page" created by PCBnew.
It is just a traditional element… for good reasons… of the design process.
In the lower right hand corner you will find some important information about the drawing. What appears here is something I need to write more about for you.
One the I'll mention now: While I don't, in general, like putting version IDs in filenames, you will find in KiCad that the practice pays you a dividend: Notice that the filename the drawing was done from/ saved in appears in the legend text. Put a version ID in the filename, and you put it on the drawing!
(This entry needs expanding! If you particularly want THIS expanded, write and cite "Page co1leg")
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This is no "answer"… but it may help you on your quest to an answer… see
Page from official KiCad documentation
… especially the material about what KiCad calls "Format Symbols". For example, the Format Symbol %Y is replaced by your company name. How do you tell KiCad what to use wherever %Y occurs? I'm not sure! And some of the Format Symbols are "special"… managed by system?… e.g. %K.
If you are using a modern-at-12/19 version of KiCad, e.g.5-1-5, there's a "Page Layout Editor" tool available from the main project manager window. Select "Show Title Block in Edit Mode" with the button in the toolbar. (It is one of a pair of alternates, the other, to the left of this, has an icon with a "T". They are to the right of the zoom choices). Zoom in on the "legend" (the info about the sheet in the lower right. You should be able to see the various Format Symbols used in generating the text in the legend.
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So… that's the question, badly expressed. After a LONG time digging around, I finally found…
https://www.pcbcart.com/article/content/KiCAD-PCB-design-tutorial.html
… and in that something finally triggered the thought I needed…
The text in the legends may well be different for schematic drawings and pcb layout drawings.
If you are in either the Schematic Layout Editor (EeSchema) or the PCB Layout Editor (PcbNew), you will find (v5-1-5) a tool button (near left end) called "Edit Page Settings"(EeSchema) or "Page settings for size and texts" (PcbNew) (Same icon in both cases)
Hurrah! Be happy!… because once you start using these you will want MORE. And the little tick box "Export to Other Sheets" will seem to be just the thing. But it doesn't seem to do what I'd hoped it would do. It won't, for instance, allow you to set the project name on the Schematic, and have the same name, automatically, appear on the PCB Layout. Or if there is a way to achieve that, I haven't found it yet. (I once worked up a complex kludge answer that involved using a special component linked to a dedicated footprint, and passing the project name/ version/ what have you in a reference or a value… can't recall details. Sorry)
(I suspect the "export to other sheets" merely copies the value you have entered to other sheets of the same sort… Schematics or PCB Layouts.) And I suspect it is a "once, now" export. I.e. it gets all Schematic sheets or PCB Layout sheets showing the same thing for the moment. If you then go and change the text in that on another sheet, that will be out of step with the others again.
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For now, the value you assign to, say, "Company" (which is represented by %Y "behind the scenes") for the Schematic is independent of what you have assigned to it in the PCB Layout. You would, of course, in the case of company, probably have the same text assigned in both cases. But keeping them in step is up to you. It isn't automatic.
