We kept growing them for 4 plant generations and they kept breeding true, then suddenly they were drastically altered into a mealy grape-style, from a super sweet, juicy, yellowish pear-cherry blend about the size of a ping-pong ball, but shaped like a butternut squash.
We even kept a separate area as far from all other tomatoes as we could for these particular plants, as we knew there was something special about them.
Unless you had a separate greenhouse then contamination with other varieties was inevitable..............