What is the number of hydrate isomers of chromium(III) chloride hexahydrate?

Assuming $$\ce{CoCl3·6H2O}$$ is an octahedral complex, the answer should be four as there can be $$0, 1, 2$$ or $$3$$ $$\ce{Cl-}$$ ligands inside the coordination sphere. However, numerous sources say the number of isomers is three discarding the case with three $$\ce{Cl-}$$ ligands inside the coordination sphere.

Only Loong's answer and another answer in a linked question say otherwise acknowledging the existence of the isomer with three $$\ce{Cl-}$$ ligands within the inner sphere. Every other place simply states that only three isomers have been experimentally discovered.

Also, in coordination isomerism too, in the case where both spheres become uncharged is ignored.

What is the reason?

• I have a copy of 5th edition- J. D. Lee, which says that 3 isomers are known. These complexes are formed when $\ce{CrCl3}$ dissolves in water. Came across an article where it is written that: If diethyl ether is added to the solution then a fourth complex $\ce{[Cr(H2O)3Cl3]}$ can be formed (without the water of crystallization). Dec 20 '19 at 13:48