First of all, LaM means AM and Sim means Bm. In the sheet music you will see below, what does mean AM________? Does it mean all the notes I will find on the _____ part will correspond to the AM chord? But if so, shouldn't it be C# instead of C?
Pic related to my comments on Tim's answer.
It is C♯! The piece is in key A major, and that has its key signature at the start of the line, including a ♯ sign on the C space. It only needs to be there to tell us that every C in the piece must be C♯.
EDIT: The key of the piece is A major. The chord/s in each bar are chords formed by the notes in that bar, or the chords which can be played in that bar. In bar 12, the first half is chord E, followed by chord D.In bar 14, the first half is chord A major, followed by 4 separate notes which don't constitute a chord. Hence solfege.
There is no key change, and that E chord you mention doesn't need a D♯ note, because the piece is still in A, which has no D♯.
