Conventional wisdom, and info from the manufacturers say an unopened bottle of brake fluid lasts 'forever', but once opened its shelf life is 6 months. I've seen plastic bottles in auto parts stores (of Dot 3 &4) with dust on them that look like something has evaporated out, collapsing the bottle. These are the bottles at the back of the shelf while new ones - same brand - in front are fully filled.DOT 4 was new unused but been on the shelf for years so used a newly bought bottle.
What you did was probably a smart move.
