That information contradicts the official warranty statement in Appendix E: Warranty on page 290 in the Dexcom G6 System User Guide which states:
“What’s Covered and for How Long?Dexcom, Inc. (“Dexcom”) provides a limited warranty to the original purchaser (“you” or “Purchaser”) that the Dexcom G6 transmitter (the “transmitter”) is free from defects in material and workmanship under normal use (“Limited Warranty”) for the period commencing on the date of first use by the original purchaser (the “Date of First Use”) and expiring three (3) months thereafter; provided, that, the Date of First use occurs within five (5) months of the date of shipment (or disbursement) of the transmitter to you (“Warranty Period”).”
I would believe that official warranty statement over the verbal advice of a Dexcom rep. You can find an on-line version of the user guide via the Dexcom web site on the warranty page https://www.dexcom.com/faqs/warranty-for-Dexcom-CGM-Systems (the user guide link is on the lower right of the page).