helen, i have just been reading through this post, it always makes me giggle when this sort of thing comes up, from my many years of studdying animal courses and cat ownership my opinion is that if they have been raised on one type of food and are perfectly happy on it for years and are heathy cats, then continue feeding the same, by swapping and switching foods around u are creating more fussy cats, they will soon learn its botiza or nothing and go back to eating it, they wont starve themselves
this is just an opinion, have had cats for 17 years and they have always eaten what they are given, they dont get a second choice if they turn their noises up, food is bought with quality and value for money in mind