As long as there is nothing conductive (not even slightly) in contact with/between/across the two faces of each coin battery they will not self-discharge any differently than when inside the retail packaging.

If there is a chance the batteries could sit for years before being used, consider some sort of marking to indicate when they were ‘new’. Battery voltage testing does not tell the whole story, an old but ‘never used’ coin battery will have less remaining charge than one manufactured quite recently.

How much self-discharge occurs varies with the battery chemistry and battery ‘type’. Alkaline vs. Silver vs. Lithium, and so on.

All this is assuming the batteries are kept in a dry location that does not get too warm. Dampness also encourages potential surface corrosion.