In 2020, Leg Bands are only for the specific use of a Breeder to keep track of 'their' breeding programs to assure that they are not over breeding their pairs and to assure that they are not inbreeding members of the same families. Once they leave the Breeder's facility, there is limited to no linkage back to a source.
Several decades ago when Parrots where 'imported' banding was common and records where maintained. Those days are now long past.
There are a couple of 'band' manufacturers' that still make bands and they maybe able to connect the number with a Breeder name, but I would not place great hope as they rarely maintain records more than a year at most.
Check the Pet Stores in your area, one may remember the name of a Breeder that used that set of letters and numbers.