Plants of the same genus look similar enough to one another that you may be able to make a good guess, but seeds vary considerably. Some seeds that are not even remotely connected look alike.
When labeling plant tags, always use a pencil or a botanical pen or marker.
Permanent markers tend to fade over time. Check your tags regularly as you walk through your garden.
The Complete Idiot's Guide to Seed Saving and Starting
Artwork: Garden Markers