Yes--once you render the files to the DVD-A folders (Video TS, etc.), those stay there until you render another project. You can just go with the "Burn" option for your additonal copies.
You can (probably should actually) use different folders for each DVD you're mastering. If you've got the space leave them there for a while, that way if you need another copy just fire up DVDA, goto Burn DVD and select the folder to burn from.