This is my understanding of it. And I've asked for clarifications from many knowledgeable Ihubbers and have yet to find one who says different.
A form T trade is one that is reported after hours, between 4:00 and 6:30 known as the extended trading period. A form is actually filed to document the trade. This was created for the NYSE, AMEX and NASDAQ exchanges.
Since many trades on the OTC and pinks are not all settled during normal business hours, they are instead settled after the close and are still referred to as "t trades". But they are NOT trades that brokers have made between a buyer and seller after the close of business.