If you don’t have the page number as a token in the filename when exporting multiple pages to single-page graphics formats (e.g. SVG, TIFF), you get some weird behaviour.
First, I get the dialog telling me that “one or more output files already exist”. If I look in the folder before dealing with the dialog, I see that Dorico has already saved the first page as a file, and is trying to write page 2 to the same filename.
If I choose “Overwrite”, each page gets saved to the same filename, so I end up only with the last page. Choosing “Create New” will give me files for each page, each file being given an index number.
If I try to export the pages again (with the first batch of files still in place) then once more “Overwrite” only updates the ‘original’ filename file with each page in turn, leaving me with the last page. If I choose “Create New”, then I get a new set of pages as well as the old set still being there!
The behaviour is logical, though perhaps unexpected. The moral of the story is: Use page numbers in the filename for separate pages.