A319 pilot reported during taxi that they got a hot brake caution ECAM message. After takeoff they determined they may have taken off in violation of the limits.

Narrative

As we were taxiing onto the runway; we received a Brakes Hot caution. We looked at the Wheel ECAM page and the hottest brake was at 300 degrees. After a brief conversation about the issue; we both concurred that a takeoff should not be performed if the brake temperature was in excess of 300 degrees. Since the temperature was at 300 and not in excess of 300; we concluded that a safe and legal takeoff could be performed so we cleared the ECAM and started the takeoff roll. After liftoff; we kept the gear down until the temperatures was well below 300. After the gear was raised; the flight continued as planned.After we reached cruise altitude; we wanted to verify we did everything correctly and didn't miss anything. Looking in the AOM under taxing procedures; there is the caution that we both referenced taxing onto the runway. The caution says Do not takeoff with brake temperatures in excess of 300°C (fans off) or 150°C (fans on)" so we complied with that caution. The sentence before that says something slightly different. It says "If fans are not used for taxi; crews may depart with indicated brake temperatures less than 300°C; as the reading will represent actual temperature." Brake fans were not used taxing out to the runway.After reading both of those sentences; we concluded there is a different limit between those two sentences and we may have taken off in violation of those limits. This event has never happened to me before; but if it happens again; delaying the takeoff and cooling the brakes would remove any ambiguity from the situation.Cause: There is no limit to the amount of safety you can apply to a flight. Limits are limits; but even if something is within limits; it might not mean it's good to go. Having brakes at that temperature just before takeoff is not normal and getting it back to a more normal range is always the more safer option. The taxi was a little longer than normal but braking was minimal. Monitoring the brake temperature wasn't on my mind because of that; but it should have been. If the caution in the AOM was tied directly to the Brakes Hot caution (example is if Brakes Hot caution is present; don't take off); it would have been more clear about what our only option was. Either way; we should have mitigated the risks by delaying the takeoff to cool the brakes."