Interesting - as there are also references to '4H' being "Fly S/A Linhas Aereas", a Brazilian airline...

I understand that IATA codes can get recycled quite quickly (6 months after the previous airline is delisted) so it is not the first time I've seen an IATA code that apparently refers to two entirely different airlines, in different parts of the world...

Amadeus Operational Info doesn't seem to find those 4H GIG-GRU flights, so I wonder if they don't really exist...