Guy Betsy is an expert on this practice. I am forever teasing him as to the number of RTW tickets he has purchased, and is using sequentially and entertwined. I can barely wrap my mind around the current 6 continent RTW OneWorld ticket that I am using. Your plan of dropping a RTW within another RTW is completely legitimate. You simply have to be careful to finish all of your travel within 12 months of the first date of travel on each ticket.