In The Unicode Standard, Lepcha script implementation is discussed in  Chapter 13 South and Central Asia-II: Other Modern Scripts.

The Lepcha script was encoded in The Unicode Standard version 5.1. The script is encoded in the following block:

BlocksCharacter RangeAdded in Unicode VersionUnicode Chart
Lepcha 1C00..1C4F 5.1  U1C00.pdf

A number of proposals for its inclusion were submitted to the Unicode Technical Committee and WG2:

1992-11-25 Róng (Lepcha) — Rick McGowan ( Unicode Technical Report #3 R2)

1999-02-11 Lepcha script (RÓNG) — Michael Everson ( L2/99-067)

2003-08-13 Lepcha, Limbu, Syloti, Saurashtra, Tai Le and Bugis Proposals — Daniel Kai ( L2/03-253)

2003-08-13 Introduction to the Lepcha Script — Daniel Kai ( L2/03-259)

2004-10-28 Proposal to encode Lepcha — Govt of India ( L2/04-397)

2005-02-04 Analysis of the Indian proposal to encode Lepcha script in the UCS — Michael Everson ( L2/05-061)

2005-02-07 Issues in Representation of Indic Scripts in Unicode (Unicode Conference Presentation) — Om Vikas ( L2/05-063)

2005-07-04 Proposal for encoding the Lepcha script in the BMP of the UCS — Michael Everson ( WG2 N2947,  L2/05-158)

2006-05-12 Letter from Government of Sikkim regarding Lepcha Encoding — India N.B. ( L2/06-220)

2008-03-02 Criteria for the encoding of script-specific dandas — Unicode and US National Body ( WG2 N3457,  L2/08-118)

2011-07-27 Lepcha Encoding model feedback — Lorna Priest ( L2/11-305)

2014-02-05 A bag of suggested improvements to Unicode’s provisional Indic properties — Roozbeh Pournader, Behdad Esfahbod ( L2/14-065)

2014-05-08 Improvements requested for Unicode Indic properties — Roozbeh Pournader ( L2/14-126)

2015-12-07 Lepcha Unicode - Published Standard — SIBLAC ( L2/15-332)

UTC #146 Minutes ( L2/16-004) (See D.6 for decision and action items)