Considering most of the other energy companies are substantially further behind than this I would not worry too much. A quick phone call will usually put a customers mind at rest since BG seems pretty good at finding applications where ever they are in the process - particularly if you have emailed the application. Tried this with EDF, EON and SSE and quite frankly their record systems are a shambles!
I had my system installed on March 26th and EDF received my paperwork and applications forms on March 30th by recorded delivery. I have had an acknowledgement letter and have spoken to them 3 times but they are still on February applications. I can't say I am bothered though as the payment will be a nice lump sum. Already generated 2090kwh so I should get at least £470 if not closer to £500 - 600 as my first payment. On an aside, system is generating + 16.5% on top of SAP calculations so lets hope they don't kick up a fuss about high readings.