I'm reasonably familiar with Inkscape but can't see the answer. However you don't know what you don't know.

I'm looking for an easy way (procedural not manual) to remove duplicate lines. Say, several boxes aligned next to each other, or cresselated shapes for a tabbed box. There are too many to go through by hand, break, remove and rejoin paths. Deepnest.io doesn't seem to think the cresselations can be fitted into each other, which is wrong as I constructed them from the same prototype object.

Am I missing anything? Is it possible?

I don't think so.

I also don't think it would be wise to nest / co-locate the finger joints, unless you want overly generous gaps. 

If the boxes are created by duplication or cloning, would deleting two adjacent sides from the original box before duplicating solve your problem?  When you juxtapose the open boxes, the interior lines that result would then be single strength.

How does a cresselation differ from a tessellation?  

@RWE2  Sorry, I meant crenellated, like a castle parapet. Tessellated, to be covered in mosaics or a repeating pattern. I also like reticulated (covered with a reticule or net) and graticulated (covered by a graticule/grid). Articulated is not nearly as an exciting word, merely meaning "jointed".

@TylerDurden My kerf is only 0.1mm so it's not really a problem to have slightly loose joints but I certainly don't want them cut twice.

I think I'll do this the manual way. Le sigh.