With all collection agencies, there is a lag period between the actual date of the use and the date of payment. The lag is normally between 6-9 months in the US, but varies on the society, the amount of royalties, type of royalties, and other factors. The lag period is this size because of all the movement of money. The society has to collect the royalties, send them to the publisher, and then the publisher (like Songtrust) needs to process the royalties and pay them to the writers.
If you have been receiving steady royalties and believe you are missing payment for a use over 9 months ago, feel free to reach out and we'd be happy to try and help you track down your royalties.