Query behavior - with regard to statistics
Auto-stats and stats per se is only one aspect. Another is the plan, the calculated selectivity, and also the fact that plans can be cached.
So imagine a plan was generated when stats were &quot;ok&quot; (along with other circumstances such as sniffed parameter values). This can now stick around for a while in cache, and even if the stats deteriorate (a bit), your &quot;good plan&quot; can linger in cache.
Then you have the aspect that autostats samples data. The larger the dataset, the smaller the part of that data set that is sampled. So even when auto-stats kicks in, with a larger dataset you may get lower quality stats.