There are no mom and pop stations that don't move volumes of fuel these days. They can't survive due to the supply costs of running a gas station. If someone isn't buying your gas you are out of business pretty quick. So old stock isn't an issue.
Also moisture and supposed contamination is filtered out before it hits your tank by multi million dollar devices installed in all gas stations. If old fuel was as widespread enough to make a difference between "Top Tier" and "normal" gas it would make the news and that hasn't been the case.
Top tier is nothing more than paying into a consortium just to get a marketing badge to make your fuel seem better than the rest.
Please don't quote Consumer (paid off by big business) reports they are not credible.
Please cite your sources. Thanks.