ADV7188 has the default register settings for "field" signal and it also supports manual programming by setting NFTOGSIGN.
1) Page48, Figure 27, Field1 is for NTSC default VS and Field settings. How does the lcount work? Where is the counter reset line, line6? Do NVBEG and NFTOG compare with the same counter lcount? If so, the F toggle should be happened at the line2 when NFTPG[4:0]=0x3 not line3.
2) Table62 is recommended user settings for NTSC. NTSC V begin = 1; V bit end = 4 and F bit = 6. But why on the Figure 28, it shows NVBEG=0x0? NVBEG=0x3 and NFTOG=0x5?