LCD exporting takes all LCD pages and writes them to the export file. If you open the .RSLCD files using Notepad for example, you can see that each page content is between similar tags like this:
... page content ...
If you have multiple RemoteSensor layouts created, and you always used Page 1 in those layouts, and exported them to separate .RSLCD files, you should have LCDPAGE1 tags (and only those, not LCDPAGE2, LCDPAGE3, etc) in all those files.
Problem is: when you import a layout, it will wipe your current layout, all pages of it, and import the page (or pages) from the .RSLCD file you select. Currently it's not possible to import a .RSLCD file into a page of your choice, so even if you alter the files to have different LCDPAGEx tags, you will only be able to import a file into a specific page but the rest of the pages will still be blank.
What you can do to overcome this limitation is to combine the .RSLCD files into a single .RSLCD file where you use multiple page tags and put the relevant content between them. For example:
... page content coming from one of your .RSLCD files ...
... page content coming from another one of your .RSLCD files ...
... page content coming from the 3rd .RSLCD file ...
That way you can combine your .RSLCD layouts to exactly the page assignment of your choice.