I've just had a look at the episode where Shirley finds Dean's blood tests and all she says is \"
You had a load of tests done after Jimbo died\" (see
here at about 7.55). It was probably kept very vague deliberately so the writers didn't paint themselves into a corner.
I don't mind the subtle retconning of Shirley's backstory. It was invented when she was a one-dimensional villain brought in to stir up the Wicks family. There was no way to know what a successful character she'd become, or that a future producer would want to thoroughly delve into her backstory. The changes add to the character and to the story in my opinion.
I'm sure giving Jade CF is being done at least partially to redeem Shirley for abandoning Jimbo when he was dying - which I'm not against at all. I always liked Shirley as a character up until the rape storyline. She was thoroughly nasty at times but Linda Henry's talents as an actress meant there was always more to Shirley than was written in the script.