I attached a portion of music by Tallis to show my problem. From the "complete" file I took the last 5 measures of the S and A staves in which a repeat occurs. I replaced the master repeat open bar way to the end to shorten the time you have to listen. By coincidence I made apparently a correct tie in the S staff to the first note in the 2nd repeat; and this staff plays OK. I tried to make the same tie in the A staff but after a lot of trials I gave up and you see the unchanged staff, which plays incorrectly.
Until now adjustment of lyrics to the score works just fine. And it still does if I type it myself. However I downloaded a nwc piece and I wanted to correct in some places where for instance I wanted a syllable to go with a number of notes instead of one. If I use in that case the trick with ";" normally the next syllable shifts to the note after the slur. But in this piece it shifts too far! In the lyrics I find no unknown characters. I removed a portion of the lyrics and typed them again: problem stays! It is a piece (Missa tempore quadrigesimae; the credo-2) with 6 whole notes/ measure.
Recently I found a program: PDF2music and PDF2music Pro. Both programs can convert a PDF document with music to its own music notation. It does not work with scanned images in PDF but only when a music part is converted to pdf. But there are a lot of pieces available in the right pdf format.
Both programs can export the piece to a number of formats, but only the Pro version to xml. Both programs can be downloaded as a free version; the payed versions have more functions.
Still, the free Pro version works when you let it export just one page at a time to a corresponding xml file. This page can be transformed to NWC with the XML2NWC tool. In the end you can combine those different nwc files to one file with the whole piece. Then you can edit the piece for your own use.
To convert a NWC file to pdf you could install Libre Office Writer (free) where you can paste the pictures made with NWC. This program has a button which exports the file directly to pdf.
When I enter a score with a keybord I start with a blanc staff without key or Tempo assignment. I enter the notes (all quarters) using only the "white" keys. Advantage: After completion you add the key to the staff and you only have to correct some notes which have should carry extra notation (like crosses etc..). While entering notes with the keybord NWC adds bar lines automatically supposing you have a 4/4 measure. To get rid of these bar lines you place a very big measure, for instance 100/4 at the front of the staff, and then with Tools, Audit, Bar lines you delete all the bar lines. Then you remove this big measure and you have a staff without key, tempo assignment or bar lines. Then you enter the correct Tempo assignment, edit the staff for note length and bar lines.
Writing it down gives the impression that it is a clumsy operation, but for me it gives the quickest results.