Part 107 UAS pilot reported they learned that UAS flights they conducted at an RC field were not covered by the COA; as previously believed.

Narrative

While I was at school in ZZZ we flew nearly weekly missions using Aircraft X and other small multi-rotor or fixed wing aircraft at the RC Field [at] ZZZ. School management/legal told us that we were cleared to operate under the field's Certificate of Authorization (COA). LAANC or a School COA were never used/achieved. I am still affiliated with the school; and was notified of this change yesterday. All flights by myself at the RC field occurred between Date - Date 1. Essentially; we trusted the school management/legal and operated under the rules of a COA that is not ours. Furthermore; this COA allows for operations up to XXX ft AGL. We operated above the UAS Facility Map maximum altitudes (of XX ft AGL) due to this misunderstanding/miscommunication. In the time since these incursions; I've flown multiple times within the Controlled Airspace of ZZZ; and have requested LAANC or applied for further coordination through DroneZone every time I've been outside of this COA area. I would estimate over 100 people have flown without authorization in this area due to the miscommunication and inability to actually read the COA we supposedly operate under. Going forward I will be requesting LAANC in any controlled airspace I am able; regardless of any existing COA or waivers; unless that COA or waiver is submitted by myself.