Two definitions of "refugee" — one for everyone, one for Palestinians
Every refugee population on earth is governed by UNHCR — the UN High Commissioner for Refugees. Palestinians have their own separate agency, UNRWA, operating under a fundamentally different definition constructed to produce fundamentally different results.
These are structurally opposite mandates. UNHCR exists to eliminate refugee status. UNRWA exists to perpetuate and expand it. Arab states deliberately negotiated UNRWA's founding terms in 1949-1950 to exclude any resettlement mandate, establish hereditary status, and keep UNRWA separate from UNHCR so that UNHCR's resolution-oriented framework would never apply.
The result: UNRWA registered camps in Hebron and Nablus — cities that never came under Israeli control in 1948, whose residents never left, and whose populations never crossed any border. "Refugee" under UNRWA simply means a Palestinian with a sufficiently recent ancestor near the territory during the relevant years.