Came back from a long trip including London, Croatia, Sydney and Hong Kong.

No DCC attempt at all in London, Croatia and Sydney, on spends made at shops, restaurants and grocery stores. All were billed in local currency without me to choose anything. At Hong Kong one local hotel attempted multiple times to DCC (making authorization when booking online, and again at check in despite I told them to bill it in HKD). It is Hang Seng machine. In the morning of check out day I saw it was still a DCCed amount showing on Chase online, so I went down to front desk and made the guy to retrieve the correct HKD billing slip given he insisted since I already circled the HKD, it should be billed in HKD but the bank information shown otherwise. I told him if he did not track it down from the accounting dept and the amount was DCCed amount I would surely dispute it. At check out, he did manage to produce a slip showing HKD was billed. A couple hours later I saw the actual billing showed up on Chase site as the correct HKD converted.
On Hang Seng's slip it actually tells you the conversion would add 2 different % padding to the amount, I forgot the description though. I dont know how this is done as I am asked to sign on the slip that had the language with both HKD and USD both showing. Then the front desk circled HKD.
2 other local hotels did not attempt to DCC despite they too made authorization and billing (one was prepaid rate). And they too, used Hang Seng as their processors. Therefore I believe the merchants have option even on the authorizations to DCC or not to DCC.
All Hong Kong eateries, shops and supermarkets do not ever attempt to DCC. All are correctly billed in HKD.