Devgandhari is one of the volume's smaller sections, drawn mainly from the later Gurus. There is a temptation to pass over sections like this with a sentence and move on to the substantial ones, and it is worth resisting, because the short sections carry a kind of evidence the long ones cannot.
A compiler constructing a system would not leave a heading standing over a handful of compositions. Symmetry is cheap to impose and the volume shows no interest in it. The presence of a rag with very little in it therefore records something specific: this measure was used, a little, by named Gurus, and the compilation preserved that fact rather than rounding it away.
The alternative approaches were both available and both were declined. The material could have been folded into a neighbouring measure, which would have tidied the volume and destroyed the information. Or the section could have been enlarged from the same Gurus' work in other measures, which would have falsified it. Neither happened.
That restraint is one of the reasons the Guru Granth Sahib is usable as a historical source about its own composition. The proportions in it are real proportions. Anyone studying which forms the third, fourth and fifth Gurus favoured can read the answer off the volume, and can do so because the compilers did not improve their material.