Wasn't that whole "meant to compliment the Vampire Killer" thing introduced in Judgment, which is non-canon? (technicality, yes)
I never liked the idea of the Vampire Killer whip needing something to compliment it, or that the Alcarde/Alucard Spear was created for the sole purpose of being second-string to the Vampire Killer deliberately. Why can't it simply be a weapon Alucard forged on his own, that just happens to be bad-ass in its own right? Not everything needs to be connected.
Yeah technically yes you would be correct it would be non cannon but with IGA's track record (going off the assumption he could be somewhat attached to Castlevania still being there is no concrete evidence that proves he isn't) of taking out games of the official time line like legacy of darkness then turning around and placing them back in it Judgment could be one day cannon.
Also you have to keep in mind that the events of Judgment are simply non cannon though the connection to each of the characters would be considered cannon.
And again in Portrait of Ruin (which is cannon and porbably where they got the idea for that conversation between Eric and Alucard in Judgment) the weapon description for the Alucard Spear is
"A spear with ties to Alucard. Once used by Eric " which you can obtain through Wind's/Eric's quests.
Soo with all that I think it is safe to assume that, according to IGA's time line, the Alucard Spear was made by Alucard to compliment the vampire killer.
Sorry your opinion differs but the point was to discuss weather you think Alucard had some knowledge of Devil Forge Mastery and that the Alucard Spear was made by that method.