The article discussed here shows examples from older versions of the Semitic alphabet, many hundreds of years before the appearance of the Ugaritic, Phoenician or Hebrew alphabets.

The reconstructed Proto-Semitic language had 29 consonants, so it is likely that the oldest Semitic alphabet also had 29 letters.

However, this cannot be known for sure, because the very few preserved inscriptions do not contain all the signs of the alphabet. Ugaritic proves that there were at least 27 letters.

At some point in time, the Semitic alphabet has split into two variants, a North-West variant and a South-West variant, the latter being used for writing various South-Arabic languages.

While the Northern and the Southern variants have diverged in their graphic forms, the most significant difference is that they have completely different orders of the letters in the alphabet. The reason for the two orders is unknown. Perhaps they have used some mnemonic technique, like reciting a poem for remembering all the letters, and the North and the South have chosen different poems.

The North-West Semitic alphabet is the one having the order alpha-beta-gamma ..., which has been inherited by many later Semitic alphabets and by the Greek, Latin and Cyrillic alphabets, in all their many variants, including the English alphabet.

The oldest Semitic alphabet for which all the letters are known, together with their alphabetic order, is the Ugaritic alphabet. In Ugaritic, two pairs of Proto-Semitic consonants have merged, so it has only 27 consonants of the original 29. Moreover, Ugaritic does not provide any information about the graphic forms of the older Semitic alphabets, because in it all the letter glyphs have been replaced with forms that can be written on cuneiform tablets.

Even so, the Ugaritic alphabet remains the most complete source of information about the Semitic alphabets that have preceded the Phoenician alphabet.

You can see the 27 letters of the Ugaritic alphabet in the Unicode, from "U+10380;UGARITIC LETTER ALPA" to "U+1039A;UGARITIC LETTER TO" (besides these 27 letters inherited from the older North-West Semitic alphabet, Ugaritic has created 3 additional special-purpose letters, appended at the end of the alphabet).

All this information can be found in the literature about the older Semitic languages from the second millennium BC, including Ugaritic, and about Proto-Semitic and comparative Afro-Asiatic linguistics.

There is abundant data demonstrating that Hebrew, Aramaic and Arabic had more than 22 consonants at the time when they have adopted the inadequate for them Phoenician alphabet with only 22 consonants. Arabic has retained 28 consonants until today, so, like Hebrew, it has multiplied the original 22 letters by combining them with diacritic signs.

If any of these languages would have adopted the older alphabet that was the source of the Ugaritic alphabet, instead of adopting the simplified Phoenician alphabet, they would have had distinct letters for their consonants since the beginning, with no need to invent later new diacritic signs.

Hebrew SIN was a lateral fricative, which is a sound that did not exist in Phoenician. When the Hebrews have adopted the Phoenician alphabet, they did not have any letter for writing SIN, so they were forced to write it with the letter SHIN, which was somewhat close in pronunciation. At that time SAMEKH was pronounced in a different way, so it would have been a worse choice.

If the Hebrews would have invented an alphabet of their own, or if they would have adopted another Semitic alphabet variant, and not the Phoenician alphabet, they would not have needed to use a single letter for multiple sounds. This was clearly not a satisfactory solution, because later they have invented the SHIN and SIN dots, to disambiguate the letter with multiple readings.