On all CRTCs, in both interlace modes, an additional line (the 625th line) is added automatically by the CRTC at the end of the even field.
Considering n raster lines for a CRTC character line, then on all CRTCs R9 must be set to n-1, regardless of the interlace settings. The exception is for CRTCs 0/3/4 in IVM mode, where R9 must be set to n-2.
==== Interlace sync mode (ISM) ====