Ya my whole point is that untill and unless you try it, you just have no idea how much fuel "time" you really have.

I'd be assuming here that other system would draw power from that generator and that more might actually join in in a REAL dr situation.

It may sound like overkill but I'd ask to try and run the whole plant on a saturday strictly off those generators. Measure the fuel before & after and see if you forgot to plug anything that actually needs to run.

Also see how fast you can get delivery from the fuel company if you run out. Depending on the disaster, they might not be able to help quickly (if at all).

We had an icesotorm in Quebec a couple years ago and it took anywhere from 1 to 6 weeks to get electricity back (yes in winter in -20 conditions).

Fuel stations and convinience stores were all raided after day 1, not withstanding all the stores that had usefull equipement to sell.