These are both markings typical on US stampless mail from the 1840s or early 1850s, so likely but not necessarily pre-philatelic. Prepayment of domestic letter postage by stamps was not required until 1856, even though the first US general issue stamps were issued in 1847.
It's a big field and the standard reference is the American Stampless Cover Catalog...which can be downloaded free from the US Philatelic Classics Society website if you dig around in the digital library.
The Charlestown is probably the 30mm CDS listed at the bottom of the town listing (so catalog value $15). Can't assess values without seeing the whole covers but the NY would probably sell for $5 and the Charlestown in the $10-15 range. there are lots of factors that go into pricing and valuing these.