Stamp World - What Numbering System Is This Site Utilizing?

Just curious.

I utilize Scott Catalog's numbering system for organizing my collection, and will utilize other numbering systems for items not cataloged by Scott.

But I was advised to use this site (see the below link to Stamp World) to assist with identifying certain items I have been experiencing problems with identification.

http://www.stampworld.com/en/

But I noticed that this site seems to be utilizing a different numbering system.

By chance are they using Michel, Yvert, SG, or something different? Or is it their own?

I do see that this site can be useful with finding necessary info (e.g. date of issue, perfs, etc) of which can assist with identifying the stamp with whatever system one is using.

Please advise.

Regards,
Stampalotapus

SW uses its own numbering system, which I believe is intended to be "open," or at least free of claims of intellectual property infringement by Amos or others. (Whether a particular catalog publisher's set of numbers is subject to IP protection, in the absence of use of trademarks such as SCOTT or others, is a separate debate of course; SW elects to avoid the debate.)

As stated in the SW FAQ:

Our catalogue number system is solely based on the day and country of issue. It starts with "1" for the first stamp issued in the particular country and then continues up for each new issue. There are a few instances where stamps of the same type or motive have been gathered under one number. Numbers could then be Spain 25, 25A, 25B, 25C.

Thank you kindly.

Regards,
Stampalotapus