f**k me you seem to know more than most of the lads on this forum..you might as well do it yourself at this rate lolYes the original render is an important factor I think.
In terms of cavity wicking - According to the technical team at Energy Saving Trust, impermpable paint would still allow the bricks to release moisture into the vented cavity but it can be a disaster with CWI as well. As the CWI stops airflow and the cavity vents are all siliconed up then condensation from the house naturaly migrates to the outer skin (no vapor barrier in old houses) where it is trapped by the paint. Moist bricks = freeze thaw cycles and cracking of render. As soon as cracks develop then the whole processes is accelerated.
I'm by no means an expert but the mortar seems to have a high lime content and fizzes with vinegar and so does the render (where it hasn't been patched with cement). I wonder what sort of mix. I'm still unsure if the render is contemporary with the house - there is a similar house on our street which is unrendered and the brickwork is still looking good.