The conventional thinking on this is, if it's an unsolicited RFP (eg, one you didn't help write) then your odds of winning the deal are nearly 0, so don't invest much effort in it at all. The "Column A" vendor almost certainly has already engaged with the company, written the RFP to make their solution the only possible winner, and then put the RFP process in motion just to "check the box" on the requirement that multiple vendor bids be solicited.
Of course there will be exceptions, but the problem is knowing which ones are the exceptions and which ones aren't...
