Many frequencies on HF have a multiple use in the aeronautical band, HFDL is often shared with normal MWARA/RDARA/LDOC voice traffic frequencies and is usually allocated to countries in different continents as to afford "minimal interference" but Mother Nature and propagation often put sway to this.
Another example of "sharing" is EIP Shannon Aeroradio in County Clare, Ireland which uses 3.413MHz USB, this frequency is also shared with San Fransisco ATC in the USA for normal voice working of aircraft in the MWARA CEP-3 region.
Similar is 6.532MHz which is shared with Shannon Radio for HFDL in Slot-10 and also allocated and used by San Fransisco ATC for MWARA CWP-1/2 voice traffic.
If you haven't already done so, print off a copy of Civilian Aero/Military HF Frequency List, updated every few months, it's not 100% accurate, some active frequencies are not listed and I have found the odd error but beside that it's excellent value to have on the table near the radio.
The Brown Monitoring Post: Civilian Aero/Military HF Frequency List via Google will get you there, last up dated 18th August 2019.
Good luck...