The first letter was the recorder used for initial recording, say a Studer A800 as an example of an analog multitrack or DASH as an example of a digital one).

The second letter was the recorder for the mixdown, i.e. usually some 2-channel system like an analog ATR-102 or Studer A80 or a digital DAT.

The third letter was the recorder for the master, which for CD by definition was always digital. In the early days usually a Sony U-matic, which funnily enough was an analog video tape format which got reused for digital audio (and is the reason for the odd 44.1 kHz sampling rate of the CD).

Edit:

The code was actually always considered a bit meaningless.

For example, you could record on a digital DASH, but mix on an analog SSL console and print the mix to a digital recorder. That would have been a DDD CD.

On the other hand, you could record on an analog A820, mix on a digital Studer desk, print the mix on an analog A80 and that would have been a AAD CD.

So, two codes indicating "pure" digital or "pure" analog, even though both processes used both technologies.

Or record on a ADAT and mix on a Yamaha 02/R, which would have been DDD but probably sounded worse than the AAD recorded on a Studer analog tape ;)

From that Wiki link-

In practice, DAD was very rare, as many companies (especially the well-known classical music labels) used digital tape recorders (which were not prohibitively more expensive than analog tape recorders) during the editing or mixing stage.

I wonder if The Nightfly has now been ruined with dynamic compression (AKA "remastered") like everything else over the last couple decades.

My CD player came with Brothers in Arms by Dire Straits, as a demo of dynamic range. That album (a digital recording) has, shamefully, been "remastered" and dynamically compressed.