I suggest reading the result 6.2.17 in the book written by A.J.Hahn and O.T.O'Meara called "The Classical Groups and K-Theory". The result is a general version of the Cartan-Dieudonné-Scherk theorem (which implies the Cartan-Diuedonné theorem). The result is stated in the language of "Quadratic spaces over form rings". The case of the defective orthogonal groups is a particular case of the general "unitary groups" $U_n(V)$.

I suggest reading the result 6.2.17 in the book written by A.J.Hahn and O.T.O'Meara called "The Classical Groups and K-Theory". The result is a general version of the Cartan-Dieudonné-Scherk theorem (which implies the Cartan-Diuedonné theorem). The result is stated in the language of "Quadratic spaces over form rings". The case of the defective orthogonal groups is a particular case of the general "unitary groups" $U_n(V)$. More precisely, in the book you find

6.2.17 Theorem. Suppose $U_n(V)$ is not a symplectic group. If $J=\mathrm{id}_R$, assume that $R$ is not $F_2$ and if $J\neq \mathrm{id}_R$, assume $R$ is not $F_4$. Let $\sigma$ in $U_n(V)$ be non-trivial and let $S$ be its residual space.

(i) If $\sigma$ is not totally isotropic, $\sigma$ is a product of $\mathrm{dim} S$ symmetries, but no fewer.

(ii) If $\sigma$ is totally isotropic, $\sigma$ is a product of $\mathrm{dim} S+2$ symmetries, but no fewer.

When $J=\mathrm{id}_R$ you can get the defective orthogonal groups and so any $\sigma$ will be a product of "symmetries" (i.e. transvections in the case of the defective orthogonal group).