Do end of year statements take longer to generate than mid-year statements?

I logged into several of my retirement accounts to download all of their most recent quarterly statements and found a few did not have their statements rendered yet for download.

Is there some seasonal thing to this, where end of year has this larger than normal demand for statement computations that have to go through review or something more involved to verify all the rolled up numbers are correct before they go into the corresponding tax forms and all that? Does the generation of those tax forms back things up possibly?