It's much easier with White, as if Black diverges in a well established position, the chances are that it's an error if it hasn't been played before, or even if it has with more results.Jonathan Bryant wrote: Clearly it doesn’t hurt, but what relevance is knowledge of theory if you don’t get a chance to play it?
As a possible approach, as a practical minimisation, you only need to know "only moves" when they are the only reasonable route to survival or when they win on the spot. Twenty moves of theory to reach a level ending could be wasted knowledge.
As regards the Metger unpin line in the Four Knights, I had previously checked in databases to find ideas for both colours. Does that count as theory, even if I hadn't consulted Marin's book?