"Black Widow" is just a name given to relatively common 41 and 42 byf lugers made by Mauser that happen to be equipped with black bakelite grips and a magazine with a pinned black base. It was coined in the USA years ago by a dealer trying to promote these Lugers as being somehow more desirable. In reality, this material change was either just a cost or materials savings measure during the war and similar vintage byf Lugers can be found with wood grips and pinned aluminum based magazines. The term "Black Widow" is very much an American invention, European collectors do not recognize it at all.
The magazine should be marked fxo 37 (stick eagle over 37) and P08 to be correct for these years.
The correct grips usually had threaded holes on the inside, reproduction grips probably do not. The East German VOPO lugers did have both black and brown bakelite grips but they are hollow on the inside and have a "bullseye" motif on the outside. These VOPO Lugers were captured by the Russians at the end of the war and were refurbished and recycled for use by the East German police. Usually they have mismatched or force matched parts and are crudely dip blued.
Since you say your grips are Bakelite and threaded, this is a very strong indication they are originals. However, because of the "Black Widow" moniker, some people feel these pistols are indeed more desirable today, so unscrupulous individuals in the US will pay silly money for these grips to try to boost the value of a byf Luger they happen to have. Unfortunately, very convincing counterfeit grips are seen in the US because of this market. In Canada, P08 Lugers have comparatively little value because of their prohibited status, so fakery is much less prevalent. If you sourced your grips in Canada, and you are positive they are Bakelite and not resin or plastic, then they are most probably real.
Check out the Jan C Stills Luger forum for a listing and images of the known variations of these grips; ht tp://luger.gunboards.com/showthread.php?8859-BLACK-GRIPS-DATA-REQUEST&highlight=black+widow
