This paper is a response to criticism by Carson (2020) concerning the age of the Unai Bapot archaeological site in the Mariana Islands. Of specific contention are supposed errors in the marine radiocarbon (14C) research reported by Petchey et al. (2017). According to Carson, this work produced marine reservoir offsets (Î”R) of suspiciously wide variance from each other ... and those results were incompatible with the site's reported stratigraphy and dating (Carson 2008) as well as with other previously calculated marine reservoir corrections in the Mariana Islands (Carson 2010: 3). This statement is misleading on all three points. Our reply discusses the problems encountered when dating shells from near-shore marine environments where terrestrial input, in particular hard water, may complicate date interpretation. We outline a cautionary tale relevant to any researcher using marine shell dates to develop regional archaeological chronologies in regions dominated by limestone.