Don’t know if this will help , but I bought a brand new Monomachine SFX-60 MKII + from online retailer 'guitarguitar.co.uk a few months ago, and have just had a look at the box it came in.
There is no mention of ‘plus’ or ‘+’ on any of the printed writing on the cardboard box , the only place it does have the ‘+’ symbol is on a very small white sticker near one of the corners where it identifies the model along with the bar code etc.
David