During the Scenic/Kyle era, the operator was required to install 2500 ties per year. It was determined that would maintain status-quo. A few times extra money was provided by the Commission to put in extra ties, in that case, an extra tie gang would be brought in/hired to do just that. I recall Kyle had such and extra gang that went around to the various RR's doing that. GBart would have had the same requirement, as to what he actually did is open for question.
Back in the "good old" days, RR's replaced ties as needed keeping the track in shape as they went. Now-a-days, the RR's seem to let things go down, then have a big project putting in a bunch of ties at once. Most operations seem to have an extra tie gang that they ship around to do this. The last/only big track improvement project on the mainline would have been changing the rail from 45 to 70 lb. in 1922, then relaying Chama-east of Osier from 70 to 85 lb. in 1938.