Long ago, some states viewed a "replay" as a form of gambling. They would cover the replay window to try to get around that.

Also may help explain why they may have still used the little light insert on the apron to help indicate that replays were still available to play.

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Well, not exactly. The lamp on the card tray indicates a "purchased" credit. Even in add-a-ball states, games were configured to give two plays for a quarter.
This lamp is a reminder that the credit you purchased with your 25c, is still available.

Not true either. In add-a-ball states, replays were disabled, and this foil was used to cover the replay unit window. I played many, many games in many locations in the '70s. and never came across any game which awarded illegal or disguised replays.

Electrically, the lamp on the lower apron indicates that there is a credit available to be played, and does not distinguish between "purchased" and "won" credits. Some games may not have the wiring necessary to winning a credit, which would limit the implications of that light. For some games, there is a full-blown credit unit which lights the light in any non-zero position, while late EMs implementing two-games-for-one-coin pricing could get by with a credit relay if there were no other ways to obtain a credit than purchase. In that latter case, one of the switches on the credit relay is devoted to lighting the credit light on the apron.
.................David Marston

In fact, I don't think any replay machines had this little lens and lamp on the card tray. They were used on add-a-balls because they didn't have the ability to "store" multiple credits via a replay unit, but could store one extra game which was indicated by the card tray lamp. There were many Williams games which were either/or (replay/add-a-ball), and these games had this lamp if configured for 2 plays/25c, but this was accomplished without using the credit reel. The foil covered the reel and may have been required by law in add-a-ball states.

I don't think I've ever come across a game which uses that lamp in conjunction with the replay unit (won credits). Every one I've seen uses an AS type unit which is tripped when a coin is inserted and allows only one extra game (purchased) to be stored and indicated by the card tray lamp.

Just for the record, I wasn't limiting my comments to Gottlieb. I agree that, as shipped, Gottlieb would not use an apron with the credit light on a replay game. There may have been some operators in some country that wanted 3-for-a-coin pricing on a game that could not award replays, but I haven't seen it. But Gottlieb also did not include a replay window mask in the little envelope that is the subject of this thread. (I bought NIB Gottlieb, Williams, and Bally games for my route in the early 1970s. I've seen what was in the documentation packets from each company.)

Gottlieb used the half-moon credit unit on New York, which is an add-a-ball game. Regarding the AS type relay, I'd want to check schematics. I know they used an AS relay to implement two-nickels-one-play, but I recall a credit relay (conventional AG type) for the lone credit on an AAB. I'll check some schematics in my file.
.................David Marston

No. That's because Gottlieb made games that were distinctly either replay, or add-a-ball versions. They didn't make games that could do either/or.
This was primarily done by Williams and Bally, because they had games that were either/or. Their dedicated "add-a-ball" games simply omitted a credit unit, but the replay games were fully capable of being converted to true add-a-ball if desired.

I've always liked Bally's "Hi-Deal", which can be simultaneously an add-a-ball and replay game!

Bally games that had the added "Shoot Again" fixture also have this ability, or at least some do.

The lamp on the apron on Grand Prix is controlled by a switch on the replay unit and lights as long as there are credits. If GP is set to AAB it shows you still have purchased credits since the window for the credit reel is covered. When set for replay it still lights ameven though you can see the credit reel. Bally games of the era did the same.

I checked some schematics for add-a-ball games. Here are my findings.
Gottlieb games with just 1-coin-per-play (coin switch starts game): Flipper Parade, Ice Show, Lariat, Card Trix. Ice Show can have an optional second chute with an AS relay for 2-nickels-1-play in addition to the dime chute.
Gottlieb games with a Credit Hold relay (AG type): Jungle King, Capt. Card, Pin Up, Gold Strike.
Gottlieb games with a Credit Unit: New York, Team One, Rock Star.
Gottlieb game with both an AS relay and Credit Hold: Neptune.
Williams games with just 1-coin-per-play (coin switch starts game): Vagabond, Palooka.
Williams games with a Credit Relay: Blast Off (as an option), Post Time, Granada, Summertime, Star Action.
Williams games with both a Credit Relay and an Alternator Relay: Roto.
Credit light on the apron works as previously described when there is a Credit Hold Relay or Credit stepper unit. I need to spend more time with Neptune to review the pricing options.
.................David Marston

Hi BogdanW
look here https://www.ipdb.org/showpic.pl?id=701&picno=8745 TWO Coin-Insertion on the machine --- and here https://www.ipdb.org/showpic.pl?id=701&picno=12531 in upper right corner we see the Replay-Counter showing 11 Replays.

Look here https://www.ipdb.org/showpic.pl?id=1828&picno=39630 - only ONE Coin-Insertion on the machine --- and here https://www.ipdb.org/showpic.pl?id=1828&picno=39623&zoom=1 in the upper right corner we see no window in the painting, no Replay-Counter visible, no Replay-Counter mounted in the pin. This Playmates pin is just "ONE Coin thrown-in - ONE Play of 5 balls started - Backglass shows '5 Balls to Play' " - the player then plays - may make "Extraball" and maybe another Extraball and more - but the counter comes down (example) 5 - 4 - 3 - (then up) - 4 - 5 - 6 - then down - 5 - 4 - 3 - 2 - 1 - Game-Over. Such a behaviour we call "Playmates is an ADD-A-BALL pin".

In the old times the manufacturers made (like Domino / Playmates) an Replay-Pin (Domino) and an ADD-A-Ball-Pin (Playmates) --- in later years they wanted to save money - making only one model --- equipped with Plugs to adjust "shall be played as an Replay-Pin" --- "shall be played somewhat as Add-A-Ball-pin, well people do not care when they only get an Extraball instead of accumulating several added Balls".

See here on Grand Prix upper left corner https://www.ipdb.org/showpic.pl?id=1072&picno=4226&zoom=1 "adjustable REPLAY or EXTRABALL (somewhat Add-A-Ball)" and further down in the picture (on the left) "Other Coin Combinations available".
So from a country "Replays not allowed" people could buy an Grand Prix with ONLY ONE Coin-Insertion - plug for ONE-COIN gives ONE-PLAY, plug for "play as Extraball is somewhat Add-A-Ball" AND THEY TAKE THIS little Window-Mask from the small envelope You show in Your post-1 - put (glue on) over the Replay-Counter-Window on the Backglass - and then smile "our country allows no Replays - pin gives no Replays and there is no Replay-Counter visible in the Backglass". Greetings Rolf