I think they do deep revision sutra by sutra (or tantra by tantra) as far as I understood from their page. however you are right about complete revision at the end.
The thing is for example Conze has become a defacto standard in PP sutra literature. So the translation of Abhisamaalamkara by Spareham largely follows his lead.
So what do we do, retranslate the all these sutras and then make sure that the vast corpus of AA commentary texts use the those sutra passages or what? It is a big question -- that is why my verdict on the thing is only OK.
For example in the tantra they released they translated camphor but did not translate "silha" which is Frankincense and related resins from trees of the Boswellia family. With just a little extra digging they could have sorted that out.