Quality control was terrible in the early CZ issues. You can go nuts (and broke) trying to amass all the different varieties and errors. I avoid them like the plague. The only exception would be 157a, which I would have to steal in order to possess.
The Thatcher Ferry Bridge Error:
The Bridge of the Americas - originally known as the Thatcher Ferry Bridge - is a road bridge in Balboa, Panama. It spans the Pacific entrance to the Panama Canal. The 4-cent Thatcher Ferry Bridge commemorative stamp (Scott #157) was issued on Columbus Day, October 12, 1962, commemorating the opening of the new bridge.
One sheet of fifty stamps without the silver ink used to depict the Bridge was released. This error made this issue the most famous Canal Zone stamp.
Three additional sheets with this error were discovered in the Philatelic Agency at Balboa, which attempted to print an additional 100,000 copies in an effort to reduce their value to collectors. However, that one released sheet was unknowingly sold in a group of 5,000 to a Boston stamp dealer, H.E. Harris, who successfully sued in federal court to stop the additional printing.
The 2022 Scott U.S. Specialized catalogue values a single unused stamp (Scott #157a) at $8,000 never hinged; $6,000 previously hinged. The National Postal Museum is in possession of two of those fifty-stamp sheets.