Deceit was the final "This Heat" record and developed out of the previous works as well as pushing our collective process into a wider zone. It was the result of work over the previous year or so, although several of the songs were already developed at the same time as the first album.
This is a text written for the reissue of "This Heat"'s second album called Deceit.
I wonder why it is not written "had been already developed" as the songs they are talking about had already been developed at the time of first album. So past simple means that some of the songs were not developed at the time of the first album and were developed after just before releasing Deceit.