As I mentioned above, mine had no boards inside it (in spite of stickers outside). Keep in mind some of these units are 30+ years old so could have had a whole host of changes inside in that time, not just the boards.
if so, why are the “K 'and” V "labels attached?
Should the sticker label be affixed if there is a corresponding module / board in it?
The stickers and internal modules were there originally. 30 years later you can see the stickers, but are the boards still inside?
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Anyone could have done anything to it since it was supplied new. The K and V stickers indicate that’s how it was configured when sold new. The boards were designed to be interchangeable, so a quarter of a century further on (at least), who knows what any subsequent owner or dealer might have changed? They may not have changed or removed the stickers. You will need to open up the pre-amp and see.
To open up, turn it over, undo all the feet. Then very carefully slide out the inner tray. Be very careful not to catch the fascia as you slide it on or out as these can be very brittle after os many years and can break easily.
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Thank you @Richard.Dane and @robert_h
ok, if only the sticker is left behind and without the module / board in it, then can the BNC connector labeled K and V still function as AUX or not at all?
Next week I’ll check what’s inside the NAC-72 and I’ll upload the photos
To use either of the BNC inputs as an AUX line input you either need NA326 link boards or else you may be able to remake any main board links, or perhaps easiest of all, just make up some short cable links (like cartridge wires) with tags to connect the correct pins.
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Thank you
To make a BNC connector labeled K, will I change it to Phono MM by buying a 322 module?
Then to make the BNC pair with the V label functioning, then I have to buy a 326 module for AUX or a 328 module for the AUX input variable, if indeed in the NAC-72 there is no module / board for the two BNC pairs.
Yes NA322 boards are correct for MM.
The easiest way around this is to get any work to fix/repair the phono functionality done at service. Darran sorted out my two 72s. As well as undertaking their first services after 23 and 28 years.
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there’s no phono box inside (323) or K
Remake the links then if you are going to use an external phono stage.
Or get some MM 322 cards. Ask Darran, he may have a pair.
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See which Naim NA3xx series boards you can find…!
A fun challenge… 
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Final issue for 3 series MM boards was NA322/4. NA322/3s are fine too but I would perhaps not go for any earlier ones than that.
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The inside photo of the NAC-72 is as follows:
There are 2 questions for the photo of the NAC-72 above:
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Do all NAC-72 inputs (Tuner, Tape 1, Tape 2) all function properly without the addition of a card / module?
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Input with BNC connector (Phono and Variable AUX) means it doesn’t work? only K, V stickers like the photo above? In order to match its function, I want to change it to: 1. BNC 1 → Phono MM 2. BNC 2 → AUX, then what card / module do I need?
Thank you
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All the other DIN inputs will function just fine.
For BNC input 1 you want a pair of NA322 “N” boards, which are for MM cartridges (see my post above).
For BNC input 2 you want either NA326 link boards, or else ask your Naim dealer to make up a pair of link wires with suitable connectors for the pins on the main board. This pic from the internet shows what the NA326 link boards look like and should help you should you wish to just go for link wires instead.
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Thank you @Richard.Dane
From my photo above:
No. 1 is for: AUX (NA 326)
No. 2 is for: Phono MM (NA 322)
For the part of the PIN I marked the yellow box for what module / board?
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Here is a pic of my (later type) 72, fully populated with its boards:
This has a set of NA322 N boards in its Phono position - and NO boards in the other position (where you can see the pins).
You seem to have something else missing in your ‘box’ position…?
Oh dear… 
Your 72 is incomplete, in anyone’s book. Sadly.
See below…
No that’s wrong. Follow the grey interconnect wires back from the BNCs to the main board and you will see the correct pins.
What did you do with the NA324 buffer boards where you have drawn your yellow rectangle? Do you have these?
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@Richard.Dane
What is the function of the Buffer Board attached to the PIN section which I marked the yellow box above?
Should this buffer board be installed?
Yes, definitely.