The letter codes are short forms of the scheme names, and this is where most of the confusion around Kerala results comes from.
Historically the weekly schemes have carried recognisable two-letter or short codes derived from their names, and long-running readers will have seen codes such as SS, KN, KR, AK, NR, W and FF attached to the well-known weekly lotteries. More recently the department has also used codes including BT, DL, SK and SM as the weekly line-up has been revised.
The critical point is that this mapping is not permanent. Kerala has renamed weekly lotteries, retired schemes, introduced new ones and reallocated draw days more than once. When that happens, codes are reassigned, and an old article stating that a particular code belongs to a particular scheme on a particular weekday can be confidently wrong. For that reason we deliberately do not publish a fixed code-to-scheme table as settled fact - the department's own site and the gazette carry the current allocation, and that is the only version worth quoting.
One specific caution, because it comes up constantly in searches: do not assume that two codes with similar letters belong to the same family, and do not assume a code you remember from a few years ago still points at the same scheme. Check the current line-up rather than relying on memory or on a page with no date on it.
Codes are short forms of the scheme names.
Names, codes and draw days have all been revised before.
Confirm the current code allocation officially, not from memory.