I noticed other non-bd sites with BdST. None of the sites (for either code) seem persuasively authoritative. References to BST are 1-off references, whereas the news site uses BdST consistently, but it's just one site. I notice that Wikipedia has been using BdST for some time. (Not that I'm saying it's a good source, and it didn't cite its references). I suggest that the lack of good references is maybe because Bengali doesn't use the Latin script? I can understand why someone may want to distinguish their abbreviation from BST though. What has been the past policy for determining these abbreviations? Particularly for non-Latin scripts, &/or where it may be difficult for us to find, read, &/or transliterate any native-language sources? -Shawn