[BansheeBill]

They probably had cork stoppers. If the bottles were stored upright the corks will shrink as they dry out and the alcohol evaporates

[Pearls Before Swine]

But, if the alcohol evaporated, won’t the bottles be half empty?

[Vlad The Inhaler]

They probably had cork stoppers. If the bottles were stored upright the corks will shrink as they dry out and the alcohol evaporates

The stoppers aren't cork.

Possibly old fashioned glass and lead?

And the contents are still clearly visible.