So he was with Lisa from 1981-1986.
His locations after NH (with Lisa):
1982-1983- Whereabouts unknown; possibly TX or CA
1984- Los Alamito, Cypress, (some list Anaheim), all in Orange County, CA
1985- Felton, Santa Cruz County, CA (alias unknown during this time)
1986- Scotts Valley, Santa Cruz County, CA
It is in or in-between these places he was with Lisa where the sightings of another child may be.
Other areas:
1987- Preston, Franklin County, ID (at some point; car theft) and possibly CA
1988- San Luis Obispo, San Luis Obispo County, CA
1990-2002- Richmond, Contra Costa County, CA