Has there ever been a Casascius with an unreadable private key? I know the earlier private keys are alphanumeric format...so those would not worry me too much compared to a qr code.
Also with the private key being under the hologram, the paper and ink are protected from any exposure to humidity and light....especially light since that would fade away ink over time. I have stamps that are over a 100 years old and still in great shape. Especially of stored in an environment with low humidity and no light.
Speaking from personal experience, I have had hundreds of Casascius coins pass through and every redeemed one/DEMO coin have never shown any degradation in terms of the private key
Adding to that, I have only ever seen one instance of a Casascius hologram having some sort of degradation... but I imagine this is due to the extensive transfer of it via shipping and storage at different humidity and temperature levels
Thanks for sharing...another thing I forgot to mention about my 100 plus year old stamps....is that these stamps also have a sticky substance on the back we call the gum...SO imagine having this gum that when wet allows the stamps to stick to envelopes on the stamp paper, and even then they are in pristine condition....also stamps that were use thru the postage system on envelopes are still intact as well.
Under the hologram is like encapsulating your paper away from the elements and the light....even better!
I also see down the line, the BTC from Cas coins and Bitbills...2011 era will itself be a collectable BITCOIN separating itself from the later Bitcoins mined.
So please keep on peeling them cas coins ye all...makes mine rarer.