Just thought I'd give you some info on your working solution. In my experience the reason that you cannot "$push" or "$addToSet" is because your target "entries" is probably an embedded object . You can only use $push, $pushAll, $addToSet on embedded arrays that is why you had to use the dot notation in order to update as you wanted...
After more testing; ive managed to find a working solution if anyone is interested.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.