Martin - how did you come up with the substitution/ transformation ? I had pen and paper out to try to work out an analogous transformation for the following model but i got hopelessly stuck:
\\Y = Ae^{-exp(-k( t - d ))}
Identifiability issues occur when (t - d) = 0 (I believe)
Edit: My code for the model is in this thread + post: Hierarchical Gompertz model
Edit 2: note t is data = time in days