Transvaal: Polity Style: 1877-1910

12 Apr 1877 the South African Republic is declared a British territory in accordance with a proclamation of Her Majesty's Special Commissioner for certain Purposes in South Africa of 12 Apr 1877 (Transvaal Government Gazette, 12 Apr 1877, Extra, pp. 1-3)
12 Apr 1877 - 8 Aug 1881 Transvaal Territory :: Transvaalsche Grondgebied [1]
8 Aug 1881 the Transvaal Territory is granted self-government, subject to the suzerainty of the British Crown, under the name of the Transvaal State in accordance with a convention signed on 3 Aug 1881 in Pretoria (effective upon the ratification by the Volksraad of the South African Republic on 8 Aug 1881) [2]
8 Aug 1884 the suzerainty of the British Crown over the Transvaal State is tacitly withdrawn in accordance with a convention signed on 27 Feb 1884 in London (effective upon the ratification by the Volksraad of the South African Republic on 8 Aug 1884)
1 Sep 1900 the territories of the South African Republic are annexed and form part of the dominions of the British Crown as the Transvaal in accordance with a proclamation of the Commander-in-Chief of the British Forces in South Africa of 1 Sep 1900 (Transvaal Government Gazette, No. 15, 5 Sep 1900, p. 294)
1 Sep 1900 - 30 May 1910 Transvaal
31 May 1902 the sovereignty of the British Crown over the South African Republic and the Orange Free State is recognized in accordance with a peace treaty signed by the representatives of the governments of the South African Republic and the Orange Free State, and by the representatives of the United Kingdom on 31 May 1902 in Pretoria (known as the Treaty of Vereeniging)
31 May 1910 the colonies of the Cape of Good Hope, Natal, the Transvaal, and the Orange River Colony constituted a legislative union under the name of the Union of South Africa on the date (31 May 1910) appointed by a royal proclamation of 2 Dec 1909 issued in accordance with the South Africa Act, 1909 | Zuid-Afrika Wet, 1909 passed by the Parliament of the United Kingdom (House of Lords on 4 Aug 1909, House of Commons on 19 Aug 1909, received royal assent on 20 Sep 1909) (Public General Acts, 1909, pp. 42-77; The London Gazette, No. 28314, 3 Dec 1909, p. 9217; The Cape of Good Hope Government Gazette, No. 9253, Extra, 15 Jan 1910, pp. 146-188; p. 200) [3]

[1] Also in official use: Transvaal Province.
[2] Upon the enactment of the Pretoria Convention, the state authority was transferred (8 Aug 1881) from the British colonial administration to the government claiming the restoration of the South African Republic since 13 Dec 1880; this government formally acting under the "suzerainty of Her Majesty" over the Transvaal State refused to use this name which appeared only in the British official documents.
[3] Full title (English): An Act to constitute the Union of South Africa (may be cited as the South Africa Act, 1909); full title (Dutch): Een Wet ter daarstelling van de Unie van Zuid-Afrika (may be cited as Zuid-Afrika Wet, 1909).