For those interested in the background of the Mountsorrel railway there is a short history at
http://heritage-centre.co.uk/visit-us/a-brief-history-of-the-railway/.
Who "owns" the line is rather confusing (with several "owners"). The Heritage Centre, quarry recreation, stations, museums, garden railway, and shunting areas (narrow and standard gauge) are run by volunteers from the Mountsorrel and Rothley Community Heritage Centre (MARCH), a separate not-for-profit company. The GCR, as mentioned, provide the rolling stock, trains and crews for the various running weekends. All ticket sales are through the GCR.
The upgrade to the signalling at Swithland was, I believe, a joint venture. MARCH raised funds and the GCR are performing the work.
No news on the MARCH website regarding the July 21/22 running days, this is likely to be announced on the GCR's website first.
I think there is still some signalling work to complete (electrical ?) at Swithland.