Gents,
I am not suggesting for one minute the ATPL material should be treated as one time only cram and forget.
Constantly returning throughout your career to revise the underpinning theoretical principles of your craft is a feature of any trade worth its salt.
However, I would wager money that there are very few professional pilots flying who know inside out, every detail of the entire syllabus off the top of their head at any given moment. (PCNs and assumed weights of passengers on different types of flight etc...) Unless you are a true anorak.
What is more important is that you are aware of gaps in your knowledge and know where to look to refill those gaps. Some areas of the syllabus will be more pertinent to different types of pilot at different stages in their career.
The OP has said he is struggling to cope with a busy lifestyle simultaneously, a situation I can certainly empathize with.
I am simply suggesting an efficient way to focus study time. As the syllabus progresses it becomes self evident which parts are more important and need to be revisited due to 'subject crossover.'