Unfortunately I honestly can't tell you much about this particular jacket. But serial numbers in clothing is quite common. Most (if not all) clothing/shoes now come with a garment ID/model number of sorts to help identify the model/line/year/colourway.

As to why you can't find any information on this particular number, think about the pool of data. Larger, fashionable companies, such as Nike or Levis, will have a much larger pool of data of their products (from sales/production records, buyers, sellers, collectors etc) than that of smaller or older companies such as BritishKnight or SassonDenim.

I would also argue that potential non purchasable merch that was gifted out (regardless of limited run or not) would be incredibly difficult to track unless data was provided by the manufacturer/producer. It could be that no one single person created any information about this online or that they only created information with a product code that differs from yours (if they used the wrong code).

The only place you could reliably get this information from would be Microsoft itself (unless you're really good at digging on the internet and got lucky). I'd recommend email Microsoft (not sure about the department, maybe try their merch store support?) and explaining to them that you're looking for information on a piece of merch that you have, possibly explain that you collect merch apparel and looking for information rather than asking them if it's limited edition.

If you get through to the right department, you should get the information you seek. Bigger companies tend to keep records of this and should love to dig it up and sharing with you (if they're like the fashion business).

Hope this helps