Reading the article on Thomas Cutbush in the current Ripperologist issue, one name leapt out at me. The father of one of the girls Cutbush was accused of stabbing in 1891 was Edward Johnson, a wholesale chemist druggist living in Kennington.....is it possible that this is the same man as Edward Johnston (sometimes Johnson) who was Dr Blackwell's assistant in Whitechapel, 1888?
Unlikely, perhaps, but I thought I'd ask anyway.
Although I haven't researched Blackwell's assistant I suspect that he was younger than Florence's father, who was born c. 1839. He was also settled at 11 Fentiman Street in 1887.