Apply it exactly the same as you would for manufacturing - i.e. previous issues of document, all relevant records, electronic records etc.
If you haven't got a copy of the Interpretation Guide then it's worth accessing Participate to read it. I'd also recommend doing the same for the Interpretation Guide for the current Food standard, as many of the clauses overlap, and it's a bit more expansive on some of the clauses (just be a bit wary that there are some subtle, and some not so subtle, differences ).
I posted a document mapping the main sections between the food and A&B standard here, so this could also be useful if you're using some of the Issue 8 guidance for extra input: https://www.ifsqn.co...clause-mapping/
As for the length of retention, it's a wonderfully ambiguous "defined period, taking into consideration any legal or customer requirements" in the standard.
It'll therefore likely be a case of considering the maximum shelf life of your products, any customer requirements (we have a few who'd like records retained for an inordinately long period, although when asked if they'd like to pay for the storage of these beyond the existing adequate timeframe they have changed their minds...).