Yes, I agree with this (and also checked that for all other designs in all other models the pairwise differences of the first and second pair of parameters (where they exist) are estimable). Nevertheless the treatment differences are estimable in the models 2, 6 and 7 for design 11.
Added model no. 9, warning for interaction and new function `nrOfParameters`.
Added model no. 9 and conversion of model strings to numbers.