Yep. One thing about manufacturing is that there are economies of scale everywhere. If we had to build a Saturn V from plans, we'd run into tons of problems. For one, the plans don't actually have everything you need to know. Tons of information is in people's heads. For a lot of the manual work, it's not even necessarily something they can explain. Building something with obsolete methods of fabrication is very difficult, but also the Saturn V was so optimized that switching materials or fabrication techniques would be very difficult. On the F-1 for example, they just barely got combustion to be stable. If you started substituting things, it's very possible it would become unstable again and they'd have to go do all the debugging they did out at the Edwards test stands again.
For almost everything, doing something a lot of times over a short period of time is way cheaper than doing something a small number of times, especially if there's a long time between them, and the employees have quit/retired and the tooling/machinery/suppliers have been disposed of, gone out of business, or moved onto other things.