Section 2.1.c (ii) VLAN Database
The vlan database is what holds all VLAN and some VTP configuration.
This database is stored as the file vlan.dat in NVRAM/flash.
Since vlan information is not entirely saved in the running or startup config, an erase of these configs will not remove vlans from the switch.
One would need to delete the vlan.dat file, AND reboot the switch to complete the removal.
delete vlan.dat
How to verify the VLANs in the database?
show vlan
Note: extended range vlans are not stored in the VLAN database
Source: https://www.fir3net.com/Switches/Cisco/the-vlan-database.html