Questioning the Meaning Model’s application to contact language interpreting

The other morning for the Master of Arts in Interpreting Studies, I read a quotation of Danica Seleskovitch’s “Théorie du Sens” or “Meaning Model” and I’m not sure it applies to sign language interpreters who interpret contact language between English speakers and bilingual English/ASL deaf signers. After all, it is not that most deaf people don’t know English; it is that they can’t hear it. The only time I do what Seleskovitch describes is when I’m interpreting for ASL monolinguals, and even in their ASL there is often some English. Is there any “pure” ASL that we can apply the Meaning Model to?