Hi,
I have found Eliza on the censuses after 1873, but not Thomas. I am using my work computer at the moment, and I haven't got all of my research with me, but off the top of my head, in the 1871 census Eliza has two sons, a George T. Pollard and a William. The only George Pollard I could find around that time in the birth indexes was a Thomas George, which I think is him. Following his mother's 1873 marriage he appears as Thomas Courtney. Rose is born in the same quarter as the marriage, seemingly registered as a Pollard, but after the marriage given as Courtney. Sarah is born 1875 I think, registered as a Courtney.
Rose did marry Charles Savery in 1891, and this does make the Hackney connection interesting. As you have seen she lived in Ada Street in Hackney in 1891. Charles Savery lived in Goring Street at the time (which is now called Jackman Street). If you look at them on a map they are neighbouring streets which run parallel to each other. You will also see that Charles' maternal grandmother is living with them, who is Eliza Hine (Eliza's mother, and so Rose's grandmother too). I can't remember what year the marriage was, but Charles Savery's father and namesake married Jane Hine, the daughter of George and Eliza.
Having seen all of this I couldn't help but wonder why George and Eliza would have left their first daughter with Eliza's parents, then got married and had more children of their own, and moved out of the area, only for Eliza to follow later on. If she was George's daughter I can't understand why they didn't take her in when they had children in wedlock. Maybe it was because of the stigma surrounding illegitimate children? Although young Eliza seemed to be happy having Thomas Courtney's children before they were married, and then another during, but kept them all together.
Matthew