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

Thaana script was first encoded in The Unicode Standard version 3.0.

Blocks Character Range Added in Unicode Version Unicode Chart
Thaana 0780..07BF 3.0  U0780.pdf

Subsequent to version 3.0, the following characters have been added to the Thaana script:

CharactersUnicode VersionDocumentation
07B1 3.2  WG2 N2264.doc/ L2/00-328

Documentation refers to  ISO Working Group and Unicode proposals

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

1992-1993 Exploratory Proposal for Maldivian (Dihevi) — Rick McGowan ( TR3-2)

1997-05-30 Thaana proposal — Jenkins/Everson (L2/97-197 (not online))

1997-05-30 Proposal for encoding the Thaana script in ISO/IEC 10646 — Michael Everson ( WG2 N1519 (unofficial HTML version of a document submitted to WG2), L2/97-036 (not online))

1998-03-10 Revised proposal for encoding the Thaana script in the BMP of ISO/IEC 10646 — Michael Everson ( WG2 N1699, L2/98-161 (not online))

1998-05-05 Part 1:Architecture and Basic Multilingual Plane AMENDMENT 24: Thaana — WG2 ( WG2 N1824thaana)

2000-04-07 Proposal to add characters for use with Thaana Script (Divehi language) — Paul Nelson, Paul Beam, Mohamed Abdul Gadir ( L2/00-120 (also references glyph shape in  WG2 N2263 page 8))

2000-09-15 Proposal for Encoding Thaana Letter Naa in the BMP (summary form) — Ken Whistler ( WG2 N2264,  L2/00-328)

2012-11-03 Sorting all RTL scripts together — Roozbeh Pournader ( L2/12-377)