Render Retaining Wall - No DPM

Hi all, looking for some advice.

We had a 5ft retaining garden wall built recently: 20m in length, built with 215mm 7.3N blocks with concrete/rebar and backing drain & weep holes.

On advice we bought some cans of blackjack to be used to DPM behind the wall, however we found after the work was done that it was never used, and no other forms of DPM were done. The back of the wall is now completely filled-in up to 5ft with stones/soil.

We’re at the point where we want to render the wall, however we’re worried without any DPM it’ll affect the longevity of any render.

Any advice on whether this is a big issue and what we can expect if we do render it, and if there is anything we can do to the wall or to the render mix to mitigate the problem ?

Thanks all