I've got a 7" shock on my Blur XC and I suspect it is too short.
According to the Blur XC specs it's got;
12.8" BB height, mine's 11.8"
16.9" chainstays, mine are 17.2"
29.6" standover, mine's 28.5"

This is all with no sag on the shock and with 130mm instead of the recommended 105mm forks.
I only realised when I went to swap the shock off my old Blur frame as a quick way of replacing the bushes and found that it was half an inch longer at 7.5".
I've been riding it like this for months without noticing anything wrong. 😳

Normal blur is 200 x 50mm the blur LT is 2oo x 57mm i think

It looks like the 7.5" shock is the right one.
I tried it and all the measurements look about right now, as does the angle of the rear shock link. I don't know how I never spotted it was angled too far forwards before.
200mm would be too long. The rear link would be angled back too far and would contact the frame.