Number ordering images

[the cartesian]

Hi, i've recently been exporting images to show number sequence for customers to easily pick 2/200, 5/200 etc using LrC. Suddenly not working. Has something changed with latest version or am I misremembering how to do it?

select files, go to slideshow, hit ABC, select sequence, return to library and export. 

Don't recall changing anything in overlay/loupe

What step have I forgotten?!

TIA, Matt

[JohanElzenga]

I'm not sure I understand what the slide show module has to do with exporting images or with adding a sequence number to exported images.