It appeared that it wasn’t possible to revise a quotation such that a new quote number and incremental version number in the title is generated. It turns out the duplicated quote displays the source quotes number, but later increments this number on save. The title must be edited by hand (this would be a nice and easy feature to add).
I did find a bug: (1) it isn’t possible to go back and edit the line item (in edit or duplicate), and adding a new item (the original is missing) results in a quote with two line items, but the grand total correctly reflecting the second.
This may not seem like a big deal, but I’ve added a score of custom fields and re-entry is very unappealing!