I wash everything, especially if I use water soluable markers because if you don't wash them thoroughly, they can be heat set, which makes them permanent, or resurface later. I finished a tote for my DMIL which I did hand embroidery on the front of. The embroidery got a real good soaking to remove the blue marker and to set the floss so it didn't run later (I used a bit of Syntropol to set the floss).
Better safe than sorry.
Cheers, Helen