This issue is all about pronunciation, with no difference in meaning. Think dialects, such as hearing people from New York, Boston, Iowa, Georgia, and Texas (or Great Britian, South Africa, Canada, Ireland, Scotland, and Wales) - all see the same word in print, but it comes out sounding quite differently when each says it.
The actual difference is not between 'Tav' and 'Samech' but rather between 'Tav' and 'Sav' - two proninciations of the same letter, depending on the notation of a dagesh (a mark denoting emphasis, strengthening, or doubling) which appears as a 'dot' in the middle of the letter. The same is true between the letters 'Bet' and 'Vet', and 'Koff' and 'Khoff', for examples. You can also find the dagesh noted in the middle of letters such as 'Bet', 'Daled', 'Mem', 'Lamed', and 'Nun' when they are strengthened, lengthened, or doubled in pronunciation. Think of the words "Shabbat", and "Siddur" - we write the transliteration in English as if there were two 'b' or 'd' sounds because of the function of the dagesh.
There are also differences in the pronunciation of the vowels, and sometimes the accented syllable: in the example you note, it is Shah-baht for the Sephardic, and Shah-baws or Shah-bos for the Ashkenazic.
Ashkenaic Jews (Jews who trace their origins back through the area of Europe today including Germany, France, Austria, Serbo-Croatia, and parts of Russia, for example, generally under Christian control in the Middle ages) have a regional dialect that was probably influenced by the languages of the region, and the widespread use of Yiddish (a mix of middle-German language and the Hebrew alphabet and vocabulary), and tend to have a pronunciation style that makes more of a distinction between the presence and absence of the dagesh.
Sephardic Jews (Jews who trace their origins back through the areas of Spain, Africa, and Asia, primarily under Muslim control in the Middle ages), follow a dialect that was influenced by the languages of that region, and the widespread use among themselves of Ladino (a mix of Romance languages, primarily Spanish, with the Hebrew alphabet and vocabulary), and tend to have a 'softer' (perhaps more sibilant) pronunciation, and less distinction between the presence and absence of the dagesh.
(As a side note, there were other languages - Judaeo-Persion, for example, which was a mix of Persian (Farsi) language with the Hebrew language and vocabulary, and which led to a different pronunciation/dialect.)
All of these dialects are derivative - they come from an earlier version of the language. Language is a living thing, and changes with use, so asking which came first doesn't really make sense. The most likely way to hear how it was pronounced in an earlier version of the language is to listen to the cognate languages and extrapolate - so if you can hear both Arabic and Aramaic speakers pronouncing similar words, and imagine what those pronunciations along with modern Hebrew might have come from, you will be on the right track. There is probably no way to know for certain; there are no recordings of proto-Semitic, Akkadian, or Ugaritic spoken, nor of early Hebrew, so we are left to guess.
You may find more information available through studies in departments of linguistics or ancient history at some universities.
Because this is not a question of Jewish values, morals, ethics, or proper behavior, this will be the only answer offered here.
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