There are changes in every issue of SKY magazine which in principle should start on the first of each month, but IME you can get last month's choices during the first few days. However, there's a lot of overlap. Note that there seems to be a difference between the movies featured in SKY for DeltaStudio and what's actually available on a given aircraft. The good news is that it's now a bit easier to quickly see the list of all DeltaStudio movies, versus having to keep clicking to see two more at a time.

The same is true for AVOD: there are changes on the first of each month, roughly, but a lot of movies are carried over so that it's far from a totally different set of selections. Also, certain aircraft types tend to have movies motivated by certain routes, for example the movies about Australia on the 777. It seems to me that the 767 generally has a shorter list of movies.