A notable era of stamps in the Philippines is the time of heavy reliance on overprinting previous issues. These usually come either as provisional surcharge overprints or commemorative overprints, which may or may not include a surcharge. The practice has more or less stopped in the 90's, where most overprints are done on souvenir sheets, generally in regards to a philatelic exhibition (some surcharges did occasionally happen, a notable one in 2000). Still, during the 70's-80's a year would not pass without an overprinted issue.
This essay will not cover early pre-cancellations of stamps for official purposes.
Overprints are usually done as a cheap means of issuing postage for a specific purpose. Rather than designing and printing an entirely new stamp issue, it's costs less to take existing stock and slapping something on top of it. There's also the need to put to use old stock, may it be surplus definitives or commemoratives that are no longer relevant. For collectors can become a headache as overprints are categorically different for the purposes of collecting.
