Other mistake: This is for the episode "Crock Tales" (the 22nd of the season). Almost all the flashback sequences are wrong in time. The one from 2003 has Niles and Daphne coming back from their honeymoon but they married in 2002. Although not ever couple take their honeymoon directly after they've married, the wedding episode "Ring Cycle" mentions them going on their honeymoon.
Continuity mistake: For "Crock Tales" (11x22). In the 2002 flashback Niles and Daphne have just slept together. Actually they first had sex in 2001.
Answer: It equals the record of James Arness of "Gunsmoke" for the actor who's played the same part on TV NOT in a soap opera. If you include soaps there are two main contenders - William Roache, who's been playing Ken Barlow in "Coronation Street" in the UK since 1960. Don Hastings has been playing Robert Hughes in US soap "As the World Turns" since 1960 as well.