I don't think there's anything fishy about your Colnago Export. I don't know much about the Export model but I think they were a lower spec. model. Is there a serial number on the right hand rear dropout? I wouldn't worry if no serial number is present - I don't think all Colnago's had serial numbers. I really don't think the serial numbers that are found on Colnago frames really mean anything to us mere mortals - perhaps they meant something to the frame shop that built them though.

Just a quick stab in the dark - I would place your frame into the early to mid 80's category. (single set of bottle cage mounts)

Painting and Chroming? The frame's paint scheme seems perfectly fine with me. I wouldn't worry if you haven't seen it before - sometimes a different paint scheme will appear. I have a Colnago with a paint scheme I've never seen before either. If you wanted to re-finish the frame I would suggest just a paint job. I would take the chrome off and just paint it. I think you would have to re-finish the raw frame to achieve a totally clean and blemish free surface to attach the chrome to in the areas you want to display with chrome - lots of work. The total frame may need to have to be chromed also (not sure about this). It would be far easier and much more economical to settle for a fully painted frame.

I suppose you have seen this image from the '82/3 catalogue?