Fascinating topic, I know. You're welcome 
So.... When I change the bedclothes I look at the pillow protectors and think ... what's the story?
Do you change them each wash and so have a spare set? And whatever about the ones on my pillows, what about those on guests' pillows? Not that we actually have any guests these days but one day in the future.... Who knows, we might have restrictions lifted and I'll be ready with my pillow protectors all clean!