The preserve harvest I believe is included in total harvest numbers but SD GF&P does not attempt to hide much when it comes to preserves, what the harvest is and how many birds they release. Preserve harvest numbers have been pretty consistent over the last 5-years while the overall harvest has been more variable.
https://gfp.sd.gov/shooting-preserves/
The released bird issue is way more complex when it comes to SD vs. anywhere else. Seems every year some newspaper does a story on it. The pheasant farms like attention and throw crazy numbers out there on how many birds they are sending to SD (which isn't supported by the GF&P data). People who hunt at the preserves go home & help perpetuate a get a limit every day in SD myth that was tough enough to do on public land even in the good years. Guys travels to SD over confident, under prepared and hunt public land only to struggle. Get frustrated and jump on the SD is overrated & tainted by released birds side of the interwebz conversations etc. etc.
Truth is freelancing on public land is a challenge everywhere but SD is still the best place to do it and some people may pass on that opportunity because of all chatter around the above....