Purity can play a factor in development of antibodies. A foreign protein (any residual bacterial proteins in high enough concentrations) can induce "signal zero" with regards to the immune system, which will make any other soluble proteins in the local environment more susceptible to eliciting an immune response, very similar to how vaccine adjuvants work. The 192aa GH (assuming it is structurally different enough) can also cause "signal zero" itself and provide an upregulated immune environment which increases the potential for any soluble proteins to elicit an immune response too....the end results would be the same, but there are two different potential "initiators".
If anti-192aa GH antibodies are formed, it's almost guaranteed that they'd also react to any other form of GH, be it 191aa or endogenous.....that's why I'm so cautious about this.