Neither Mandos (The Large Numeral Obliterations of Guatemala, Special Supplement to EQ, 1954) nor Gruson (The Postal Markings of Guatemala, 2004) mention Panzós in their listings of the cities assigned to the Large Numeral Obliterations. Both mention that several of the numbers do not have assigned cities, as no covers with those cancels had been discovered. Neither is G1 helpful. In an article in EQ (#248, October 1985), Gerald Kendall suggests that CNL4A was Panzós until it was transferred to Antiqua in 1881.
Can you tell what Type your cancel is? What is the date on the cover? Can you post a scan?
Eric Dyck
Librarian and Website Administrator
ISGC