I've found that people keep repeating this but it doesn't work. So a couple of places in our office have permanent marker marks with smudges all around it from where someone tried to wipe it off with alcohol then a dry-erase marker.
I've found the opposite, IME; perhaps the issue is with your boards? We regularly have this happen at work and the permanent marker is always removed. It also works on plastic containers - I've successfully done this hundreds of times on both reusable plastic bins for my food at work, as well as items I buy (and resell) from Goodwills and Savers / Value Villages. I've not yet run across a plastic container that this hasn't worked on.
I've obviously not tried this with "hundreds" of whiteboards, but the one we have on the fridge at home works as well as the several size and types we have at work.
Drawing over permanent marker with a white board marker does work provided the permanent marker hasn't dried yet.
Or, at least, I have done this successfully before now - so my current working assumption is "people are waiting too long after which it doesn't work", but since I like my white boards I'm unwilling to run the necessary experiments to test this.
I don't think time has anything to do with it. Rather it's the solvent in the dry erase marker. I used to use dry erase markers to remove extension numbers from the little tabs on 66 blocks back in the days before IP phones. Sometimes those numbers had been there for 15+ years.
So, my advice would be: if one brand of dry erase marker doesn't remove your permanent marker mark, try a different brand. I think I used Expo.
