Sounds like
ollie_a hit the nail on the head.
Here in the
Shanwick OCA we use ADS-C and also CPDLC, but I understand any distinction between the systems is not obvious for those looking at the FMC display.
With some carriers, we'll often see an ADS-C position report come down, shortly followed by a crew input CPDLC position report, which needless to say isn't required. (This CPDLC report can even be
scrambled by our own kit so as to make it unusable by the controller; the LAT/LONG appearing as XXXX thereby forcing us to work from HF voice or ADS-C reports only). Those reports input manually by the crew and downlinked in the CPDLC format are therefore not used by EGGX.
We also have the ability with ADS to 'Demand' a report, in addition to those for significant points already set up in the contract. (This has on occasion caught out crews who don't realise that even in mid-Ocean
big-brother may be watching
). Emergency settings, if selected, can also increase the frequency of the contract - useful for turn-back/diversion situations.
Sounds very much as though the different procedures, as
ollie_a suggests, is due to differences in both the FANS systems in place and the operating techniques on the part of ATC providers concerned.