Hi Jeff,
Yes, you have to be careful 0f specs listed for the modules you have and what info is pulled up through the ModularGrid entries. Some of the modules have been entered by individuals and shops and there is always that demon called "typo." I generally use the figures as a guideline; but, always double check the module manufacturer's specs to make sure. These values are also steady state values and do not reflect startup loading on the power supplies. They even make adapter modules that delay the start up of modules in order to minimize the extreme loading condions on rack power up.
Power Supplies themselves along with Powered Racks are animals unto themselves and as you pointed out, many are not listed due to variety, the nature of the bus structures, and other factors. I could be wrong; but, I view ModularGrid as a planning and layout tool foremost, with the added features of calculating module loads on the busses as a secondary feature. Like most things, MG is still a growing product/tool backed by a large user community. Things progress slowly and matters are not helped much by the comings and goings of module manufacturers and limited module production runs.
So, when all else fails, I always keep a spreadsheet of everything to make sure I stay under my self-imposed 80% loading rule per rack row. I prefer to use the non-powered racks and supply my own P/S modules and PSUs ... one per rack row using the TipTop Audio uZEUS modules. This gives me an advantage of only turning power on for the rows of modules I might be using as opposed to the whole thing sitting in standby mode doing nothing. The disadvantage would be that my setup is not very portable which does not appeal to most musicians. There again though, this is one of my home hobbies and not a profession that tromps around from one venue to another.
In the end, I use MG more for module and rack layouts more than anything else and the reports as a quick calc on P/S requirements. Then my spreadsheet kicks in ... both the one tracking rack electrical loadings, and the other tracking expenditures, LOL.