A character's past history does not need to be fully defined at the start of play. Blank years may be left in the character's background, leaving an air of undefined mystery about what the character did in that period.
At some point during later play, before the start of an adventure, the referee and the player concerned may discuss revealing some of this mystery background, through the character taking on a new background bonus to reflect what he/she was doing during those years. Taking on the new background bonus will provide the character with additional cps, but require expenditure on skills is partly funded by the background bonus and partly by other additional disadvantages taken at the same time or spending of unspent experience points.
For example, a party of adventurers is setting out on a maritime adventure. Despite never showing any such skills in the past, one of the characters, a warrior, starts demonstrating boating and swimming skills. Later, an old enemy turns up and reveals that for 3 years the character was a pirate. In between adventures, the referee discussed with the character's player that the next adventure would be set at sea, and and they agreed the relevation that the character had been a pirate would be an interesting addition to the character's background. They agreed the character would backfill with a background of "A few years as pirate", worth 6 cps. The new back-filled background bonus required the character to spend 12 cps (3 cps each on two primary skills, Swimming and Navigation, and 2 cps each on 3 secondary skills, Athletics, Combat and Intimidation). To fund the 6 cps difference, the referee suggested an old enemy from the piracy days (who would then turn up on the adventure). The balance was funded by the character's unspent experience points.