CST, IST, BST — short labels that are not unique and should never be parsed.
Abbreviations like EST, CET and IST are how people write time zones and are unsuitable for anything mechanical. They are not registered, not unique, and not stable.
IST is Indian Standard Time, Irish Standard Time and Israel Standard Time. CST is Central Standard Time in North America and China Standard Time in Asia, which are fourteen hours apart. BST is British Summer Time, and was also Bangladesh Standard Time.
A system that parses an abbreviation is guessing. Use an IANA identifier for storage and interchange, and keep the abbreviation for display, where a human has the context to disambiguate it.
IANA identifiers are unique and stable, which is exactly what abbreviations are not. Store the identifier and display the abbreviation.
See also iana time zone · utc offset · standard time
We hold this as not stored — the corpus keeps IANA identifiers. See what we hold.