Thanks Seng. Atta Vimokka is explained in the Maha Parinibbana Sutta. The link to the pali is; https://www.ancient-buddhist-texts.net/Buddhist-Texts/D16-Mahaparinibbana/22-Vimokkha.htm
In the Puggala pannatti, a panna vimutta person is explained to be someone who attains nibbana through wisdom (panna) without experiencing the “atta vimokko”.
So when considering both these explanations the term “atta vimokko” (atta vimokka) can be taken to mean the 8 jhana while vimutta (vimukta) can be taken to mean becoming free (nibbana) like Lal has explained.
Any other ideas? or other places anyone has come across these terms?