While some of the original shop drawings have been preserved it would be impractical to save all locomotive drawings from any of the major builders. Every single different part on each class of locomotive would have at least one drawing, and sometimes several. A complete set of drawings needed to build a locomotive would easily fill a large drawing case.
Just a for instance using the drivers on an 8 coupled locomotive. The two main driver wheels would have a drawing so the foundry could cast the centers (There actually may be many drawings to show the detail of each of the openings on a Boxpox or Scullen Disc center). The other two middle drivers would be on a separate drawing for the driver centers (if there are no detail take offs). And if you are lucky, the end drivers are identical and you get 4 driver centers for one drawing (or one set of drawings if there are detail drawings). And to top that off you need another drawing for the tires for all eight drivers. So we have at least 4 (or more) drawings and only 16 of the thousands of parts. We haven't even gotten to the axles, rods, pins, bearings, shims, crossheads, the nuts that hold the rods, the cotter pins that hold the nuts, etc. Each one of those that is even slightly different than any of the others needs a separate drawing or drawings depending on the complexity of the part.
Then there is all the parts that go into the leading and training trucks and the rest of the locomotive.
Granted that a number of drawings will be common to a number of different types of locomotives. But if you want the drawing set to recreate a "modern" steam locomotive you will be dealing with many hundreds of drawings.
