Flood plain maps are political. They need to be approved by the communities affected before becoming official documents. I don't think you can use them officially before that happens.
It may be different in other parts of the country but county and city managers and elected officials need to approve them here.
That being said, if you have a set of maps pre-approval I don't see how advising a client about what may be coming up in the future could be unethical, you would need to explain the process to them.
I had two family members working in politics back when the last batch of flood maps came out. The two big issues they were swamped with: a cable provider not renewing the network that broadcast the Denver Broncos and the impact of the flood maps.
The most recent version for everything in my county was officially updated in 2010. The data was locked down about five years earlier so the approval process could begin. Sometime in 2008 was when the newspapers carried the story and numerous public hearings were announced and held.
The problem? We sustained a major flood event in 2007. In areas it was more than two feet higher than the old BFE, causing very substantial damage. People assume that data was used to set the new BFE announced in 2010. Wrong.
So, the general public assumes the current BFE will hold for decades into the future and build just a tad higher than the 2010 number. We counsel them to go two to three feet higher and tell the story of why the BFE will be different in a few years, should a new FIRM come out that soon. One county to the west, in 2007, experienced over 8 feet of water above the BFE of the map in place.
Whatever you do ALWAYS keep the revised maps. There was a MAJOR revision here where I live several years ago. About two years before the effective date we had done a survey with the statement that the property was not in the flood zone. Fast forward about 5 years to when the owner attempts to sell the home. The new survey showed that the property WAS in the flood zone according to the new maps, and the sale fell through. Out come the lawyers demanding we pay for the "Erroneous" statement. When I produced the map we used (the panel number and the effective date were on the flood statement) they realized the "error of their ways" and the lawsuit went away.
They aren't flood maps, they don't show what's going to flood. I've seen them show the high ground in the flood zone and the low ground out. The edge of the flood zone is some guy's magic marker art. They are only for figuring out flood insurance rates.