I have a Brown capsule for the Fall and Spring. I do have a brown leather bag that is not in finds.

I have a complete olive capsule for the summer, but I need olive footwear and cognac bottoms for the cooler months.

My main neutrals are white, grey, navy and black, and while I feel it useful
to have at least one neutral item in each category, it is not a goal to have ALL kinds of items in the SAME neutral. For instance, I don't want to wear black turtlenecks, I avoid scarves, hats,
and umbrellas in any dark neutral, and I see no need for white footwear in winter.

I can make realistic outfits with black, white and fawn. I have worn all of these. My bag is off white rather than white or fawn and not the bag I would choose with the white in reality.

I don't have a navy bag but can do boots, dark denim jeans and navy top though.

I prefer the white or the black to the fawn though - I think they feel a bit crisper.

I have a complete capsule in dark chocolate brown & in orange. Make of that what you will

@StyleFan's denim comment makes me think the best way to check if you have a complete capsule may be to make an entire outfit from one colour. Possible YLF challenge, perhaps?