[tom]

do they really polish them to match on molecular level?

Yes, that's the question. But we have solutions for both anyway.

[Rickyx]

What Maxwell consider coplanar? I mean... 0.0001 mm is considered coplanar or still separate entity?

Interested in this test as often, also in architecture, if you want correct model you deal with this stinker.
(es. Herzog De Meuron's Pipe)

And more from Wikipedia:

In a cemented doublet, the lenses are held together by an adhesive, such as optically transparent epoxy. Canada balsam was traditionally used for this purpose. Some doublets use no adhesive between the lenses, relying on external fixturing to hold them together. These are called air-spaced doublets.

So we need a third layer of "optically transparent epoxy" ...