Steven Bingham was the individual who discovered the first Denver mint-marked specimen. Denver examples seem to much more difficult to obtain than Philadelphia examples.
not true, "Since that initial discovery seven different transitional working dies have been identified for the 1988 P-Mint cents in the Wexler Die Variety Files. They are identified as 1988 1¢ WTRD-001 through WTRD-007." http://doubleddie.com/58348.html