I feel as though I should have wondered about this before, but I did not... 1960s 2000-series models (Consort, Princess, Night Lite, Med. Series, Executive) all take a 15-watt "sewing machine" type bulb, which has an intermediate (c-9) base. The Consort and other table models use a ceramic C-9 socket. The 4000 or Royal series models (Regency/Royal, Empress) use a 30-watt R-type reflector bulb, same as goes in a squiggle Aristocrat or Decorator - this is a "medium" base bulb. The Empress base I've examined has a special medium-base plastic socket which has a rotary switch as part of the bottom mounting bracket. But I've never seen a socket of this type for an intermediate/C-9 base. I examined my Princess, which does use a C-9 "sewing machine" bulb. Anyone guess where this is going...?
...yeah... it has a medium base socket, same as the Empress, with an ordinary medium-to-intermediate reducer screwed into it. Creative thinking by the factory to get around this little issue. Having never removed the metal reflector in mine, I had never noticed... until just now. I think this is the only example of this sort of thing I've seen in Lava.
P.S. Also notable how many different bulbs the lamps have used.
1960s Aristocrats/Decorator and 4000 series: 30-watt medium-base R-20 flood
2000 series, all GemLite models: 15-watt C-9 base tubular "sewing machine"
Century, 1970s-and-newer Aristocrat, Lava Coach Lantern and all Enchantress/32 oz. models: 40-watt medium base "appliance"
Imperial: 500-watt medium-base reflector flood
Carlisle, Saturna, Aladdins Lamp: 40-watt C-9 base "hi intensity"
Mediterranean, Capri, Mystique, Continental (lava only): 25-watt C-9 base tubular
That's a lot of bulbs...