First and foremost, the value guide is just that: a guide.
For notes where the guide suggests a value less than face value, the value is face value.
Regarding changes, the current value guide is simple and easy, just as it should be. Frankly, your suggested method is more complex and won't fly.
Logged
BWJM, F.O.N.A.
Life Member of CPMS, RCNA, ONA, ANA, IBNS, WCS.
President, IBNS Ontario Chapter.
Treasurer, Waterloo Coin Society.
Show Chair, Cambridge Coin Show.
Fellow of the Ontario Numismatic Association.