After establishing a suit that will most probably be trump, more often than not the King of trumps will be as important as any of the Aces. For Keycard Blackwood, assume that King to be an Ace. (Five aces in this deck!? Well, let's call them "Keycards".) Even the Queen of trumps gets special treatment.     

In Keycard Gerber, the bid of 4 asks about Aces AND the King and Queen of Trump.

     Two variants of Keycard are often called 1430 (pronounced "fourteen thirty") and 3014 ("thirty fourteen").
Responses, playing 1430, after an asking 4:

1430 Keycard Blackwood Responses :

4 shows: 1 or 4 Keycards 4 shows: 3 or 0 Keycards 4 shows: 2 Keycards without Queen of Trumps 4N shows: 2 Keycards with Queen of Trumps 5 shows: 2 or 4 Keycards with a Useful Void 5// shows: 1 or 3 Keycards with a Useful Void

Why agree to play Keycard Gerber when you're already playing Keycard Blackwood?
They shouldn't both be in effect on the same hand. It's one or the other.
Keycard Gerber is in effect after NT openings or rebids. Otherwise Keycard Blackwood is. They're mutually exclusive.

1N Pass 2* Pass 2 Pass 4

K

A

The Q IS NOT a keycard, but you might be able to show it.
Previously you might have used 4 to show club shortness. Now it asks for Keycards in the implied trump suit, hearts.

1N Pass 4

This is the important "quantitative ask".
Opener (usually 15-17) PASSes with a minimum OR bids 6N with a maximum.

Super Accepts

1N Pass 2* Pass 3 Pass 4

Here Opener skips a level to show 4+ hearts and a maximum.
Is the enthused Responder cuebidding or Keycard Gerbering?
Does there have to be a skip to 4 for Gerber to be in effect in your partnership ?
Would 4N have been quantitative despite an implicit 9+ card trump fit? What would 4 have been?

Jumps from NT with clubs implicitly trump if no other has been suggested is my choice.
In the above auction then, 4 is a cuebid, 4N would have been Keycard and 4 would have been "Exclusion Keycard" for spades, Keycard Gerber not in effect because a quantitative 4N given a known 9+ card trump fit isn't useful as an alternatively lost 4 cuebid.

Exclusion Keycard asks for Keycards outside of a suit, suggesting a void in that suit.
It's back to 4 Aces with a real Ace disqualified and the K and Q of trumps still important.

In the auction:

1N Pass 4 Pass ?

Clubs can be your default Keycard Gerber trump suit if there are no other implied suits.
Keycards in clubs include A,A,A A and K.
The Q IS NOT a keycard, but you might be able to show it.

Hand 1:	Axxx	KJx	KJx	QJx	would respond 4, 1/4 keycards
Hand 2:	Axxx	AJx	AJx	QJx	would respond 4, 3/0 keycards
Hand 3:	Axxx	AQx	KQx	Jxx	would respond 4, 2 keycards withOUT the trump Q
Hand 4:	Axxx	AJx	KJx	QJx	would respond 4N, 2 keycards WITH the trump Q
Hand 5:	Axxx	AJx	Axx	Axx	would respond 4, 1/4 keycards
Hand 6:	KQxx	KQx	KQxx	Qx	would respond 4, 3/0 keycards

In Hands 1, 2 and 6 Responder holds the Q of trumps but can't show it unless partner asks for it specifically by bidding the suit above the keycard showing response (if that suit is not trumps and there is at least another step before trump).

     With Hand 1, the auction might proceed:

1N Pass 4 Pass 4 Pass 4 Pass 5 Pass 7N Pass Pass Pass

4 asks for keycards in clubs
4 promised 1 or 4
4 asked for the Q
5 promised Q, showed K, and denied the K that lower level (cheaper) 4 alternative would have shown.

Since Opener is always bidding NT, there are never useful voids to show in this version of Keycard Gerber.

Good partnerships can distinguish between whether 1 or 4 keycards are held, but some cater to the uncertainty by having the Keycard responder bid 5 of the agreed suit if 0/1 keycards aren't sufficient for slam.
Responders with 3/4 keycards bid on, perhaps showing a cheapest king (in contrast to regular Blackwood when the 4NT bidder sets the contract.)