Model B - Knock off?

[drbytes]

Hi

So I've bought a model B with no history, I don't know the previous owner, it sat in a 2nd hand shop and I just wanted it.
The rower looks like a model B but there are no stickers on it (like i had on my previous C) and there's no PM, it also looks that there never was a PM on it.

Is this a knock off, does anybody know whether there were copies built? If so, what could I look for to verify it's a real model b?
Were there any model B's sold without a PM? (and if so, is it still possible to retrofit a pm?)

Loads of questions, thanks for any help

[Citroen]

http://www.concept2.com/service/indoor-rowers/model-b

Some early models had a PM1, later models had a PM2. You can retrofit a PM3/PM4 or PM5 to a model B. There probably weren't any fakes at that time. Have a look for a serial number to convince yourself it's genuine.