Up to date as of December 2019.

Source of this thread are the information posted on this forum, a FlightGlobal article and the excellent article from Aircraft Interior International from November 2011. This articles shows pictures and explains the details of the new cabin and the retrofitting processes. This thread however provides an update on the original timing that was communicated back then by TG.

New First (9 seats), Business and Economy class (74N):
Complete:
HS-TGA, - Still flying, mostly international where F is sold as F, including SYD,
HS-TGB, - Still flying, mostly international where F is sold as F, including SYD,
HS-TGF, - Inactive / runway excursion in Oct 2018,
HS-TGG, - Still flying, mostly domestic, international as 2x class and international where F is sold as F,
HS-TGY, - Inactive,
HS-TGZ. - Still flying, mostly domestic, international as 2x class and international where F is sold as F.

Trip report of the 9 seats F here and here.

Recent First (10 seats) and Business but newly retrofitted Economy class with AVOD (74R):
Complete:
HS-TGO, - Still flying, mostly domestic and international as 2x class,
HS-TGP, - Still flying, mostly domestic and international as 2x class,
HS-TGR, - Inactive,
HS-TGT, - Inactive,
HS-TGW, - Still flying, mostly domestic and international as 2x class,
HS-TGX. - Still flying, mostly domestic and international as 2x class.

Trip report of the 10 seats F: Part 1 / Part 2 / Part 3

F seats on 747 2x class operated flights:
F seating is now sold as preferred seating on 747 operating as 2x class (both domestically and internationally). Details here.

Other old 747s at Thai:
744: Have been converted to freighter: HS-TGH, J. Both are now retired.
744: Retired: HS-TGK, L, M, N. These were never retrofitted. They had the same F (10 seats) and C than the 74R above and an old M cabin without AVOD. All retired.

Conclusion: the complete retrofitting (F+C+M) of 6x 747-400 in Thai's fleet is complete as of January 2013, almost 3 years after its announcement, these are the "74N". The other 747-400s in Thai's fleet have somewhat recent and decent product in F and C (by comparison to pre-2013 standards) and a newly retrofitted M, these are the "74R". Phasing out of the type is ongoing, however it was announced in 2015, then cancelled then again several times after that. At this date (December 2019), TG still operates the 747-400.