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On that note, we can't discredit the Imperium or at least the Mechanicus' ability too much.
Cawls new hover tank with its fancy guns and other bits is, in an Imperium that collectively shat its pants, got torn in half, and is in a worse position technologically and logistically than it's ever been, was able to be fielded, maintained, and repaired by virtually any space marine chapter in the galaxy even those trapped on the other side of the Great Rift.
Though, he may have given the actual designs in STC format to every chapter that wanted it. I doubt we want to give every detail of our designs, but we can in the very least also sell them the means to repair them.