EDIT Related Characters
Derived from U+0E1E by extending the tail upwards. This change has been inherited from the Sukhothai script by Lao U+0E9F and Tai Viet U+AAA1.

This derivation was copied in the derivation of Tai Tham U+1A3C from U+1A3B, and this is reflected in the form of U+199D in the derived New Tai Lue script. New Tai Lue is U+1997 is derived not from U+1A3B, but its geminate form ᨻᩛ U+1A3B U+1A5B.

 Richard W