Pre-ordered Cod Infinite Warefare Digital Legacy edition but no credits have appeared or are ...

Did you preorder digitally or as a physical disc from microsoftstore.com? Digital orders are not eligible for that offer.

If you did preorder from microsoftstore.com keep in mind the credits should show as pending about 10-15 business days after the game shipped. So there are still a few days before they should show as pending.

Hello Above Nike,

The offer for 15,000 Credits for a single pre-order is only for physical (disc) purchases made off the MicrosoftStore.com site. Since your purchase was digital, it did not qualify for that offer. However, it did award one punch on the Games on Demand punchcard.
That offer requires the purchase of three eligible titles in order to complete the offer and receive Credits.

Hey there reddaro,

Since this is a disc copy and not a digital download of the Call of Duty Infinite Warfare, the console looks for the specific disc to know that you have the license for Call of Duty 4 Remastered according to Activision's support page

HERE.

"Xbox One

For disc-based (physical) Legacy and Legacy Pro Editions of Infinite Warfare on Xbox One, Call of Duty: Modern Warfare Remastered is included on the Infinite Warfare disc and no voucher code is required.
Before Modern Warfare Remastered can be played, an additional download is required. An internet connection is required to download content. The game disc must be inserted to play Modern Warfare Remastered.

For Digital Legacy and Digital Deluxe Editions of Infinite Warfare on Xbox One, there is no game disc or voucher code. An internet connection is required to download content. Modern Warfare Remastered and Infinite Warfare
are two separate downloads and there is no requirement to have both installed in order to play either piece of content. No game disc is required if you purchased the Digital Legacy or Digital Deluxe Edition of Infinite Warfare."

So unfortunately it looks like you'll need to purchase the Legacy or Legacy Pro edition via a disc or Digital Legacy or Digital Deluxe to be able to play Modern Warfare Remastered again. Though you might fall under Activision's Disc Replacement program

HERE. It's worth taking a look to see if you qualify for that program.

I hope that helps and answered your question!

Is it a game disc or digital game pre-ordered online?

If game disc, there should be a beta game code but for a limited time and also from the participating retailers only

If digital pre-purchase/pre-order, you should be eligible already. Kindly check this link.

COD Infinite Warfare Beta Faq

Since you preordered before the offer began, your preorder is not eligible.

PRE-ORDER/ORDER THE GAME

Pre-order or order any digital version of Forza Motorsport 7 (includes Standard, Deluxe, and Ultimate Edition) from the Xbox Store between September 18 and October 13 to earn 10 additional keys and 5,000 Rewards Credits. Please note that it can take
up to 96 hours for your keys from this action to appear on the site. If they haven’t appeared by the end of the contest on October 13, you will have until October 20 to use them.

it does not say that on the webpage and there is this from the official rules "Pre-order or Purchase the digital format of Forza Motorsport 7 (Standard, Deluxe, or Ultimate Edition):

Pre-order: By October 2, 2017"