I have a quick question about the letters in the uthmani script that have no marking on them.

Question
Assalaamu alaykum

I have a quick question about the letters in the uthmani script that have no marking on them. Does this mean that they are merged in to the letter that follows it and the extent of the merging depends on the letter itself and the letter that follows it. If it is a complete merging the next letter carries a shaddah if not it just carries its vowel. Is my understanding correct or have I missed something.

Jazak Allahu Khayran for all your help and my He bless this great project.
Wasalaam

Answer
Wa alaikum assalaam wa rahmatullahi wa barakaatuh
Your statement is not always correct, but usually correct.  The noon saakinah of the ikhfa' also has no sukoon marking on it. 
The vowels are part of the enhancements done by later scholars to assist the Muslims in proper recitation, and not part of the original 'Uthmani mushaf. 
Wa iyyaakum.
Wa assalaam alaikum wa rahmatullah.