I am georectifying scanned versions of Survey of India maps, which are in Everest spheroid and india_nepal datum. The exact parameters are:
+proj=longlat +a=6377301.243 +b=6356100.2284 +towgs84=295,736,257,0,0,0,0 +no_defs
I encountered two issues, one minor and one more significant.
I define a custom CRS using these parameters. Give it a name "Everest_India_Nepal_custom". Save the CRS. Use it when georectifying a toposheet. Save the toposheet with this new CRS. (gtif file). But when I reopen that gtif file in a new project, its properties show the CRS parameters, but do not show the custom name I had given for ease of recognition. When saving it said :User 100001: Everest... But when opeining it says "User 100009: *Generated CRS....". So it does not remember the name I gave. Although the name still shows up in CRS options.
bigger problem: if I try to validate this custom CRS by using the "calculate" button at the bottom of the custom CRS window, i get rubbish. But the CRS definition is correct, and it works--when my rectified topo is placed on google earth, it sits perfectly (error <10m).