You used the word "resumes," but did CX ever fly to PNH before?

Dragon did, twice daily.

I know KA did, but for CX, this is a new destination.

CX is to absorb another route previously operated by KA. It is the route to Kolkata, India (CCU).
https://www.flightradar24.com/data/flights/cx689

What's in a name, just (somewhat) the aircraft type, the colors, the staff payment level, though regarding passengers and freight, it does not matter.

If you are talking about cases like KUL and PEN, sure, but PNH was a KA-legacy destination that was launched way before the merger with CX and a destination CX never served, at least not regularly, before.

Of course, though the most relevant aspect would be the continuation of the existing connection, whether that be CX or KA, tail color, etc, that's all secondary.

https://cimg2.ibsrv.net/gimg/www.fly...95367d0cca.jpg
Another ex-KA destination in Mainland China, Chengdu (CTU) is to be resumed by CX. CX will start to operate HKG-CTU in the 2021 Summer season. At first there will be 3 weekly cargo-only flights from April 2, and then 1 weekly passenger service will be started on April 21.

Funny they list the possible connections but all of them are as bad as it can get. All except JFK means an overnight connection airside of HKG and even JFK is late night meaning something around 10hrs.

Well, they already said "Valid connections within 24-hours". What else can you expect in the presence of the pandemic?

CX traditionally uses CX9xx for Philippine flights and CX3xx for Mainland China flights (as well as some more recent European destinations). I guess this means CX will now also use CX9xx for Mainland China flights, which understandably has the most unused numbers available..

What's the general systematic behind CX flight numbers?

CX0xx Cargo
CX1xx Australia / NZ destinations
CX2xx Europe destinations
CX3xx Mainland China + more recent Europe destinations
CX4xx Taiwan /Japan (via TW only) / Korea destinations
CX5xx Taiwan (for JP flights with TW stopover only) / Japan destinations
CX6xx India / Malaysia (PEN only) / Singapore (newer flights only) / Thailand (newer BKK flights only) / Cambodia (just taken over from KA) / Israel destinations
CX7xx Thailand / Singapore / Malaysia (KUL only) / Indonesia / Sri Lanka / Pakistan (suspended) / Vietnam / Middle East / South Africa destinations
CX8xx US / Canada destinations
CX9xx The Philippines / Mainland China (those taken over from KA only) destinations

Two ex-KA destinations in Mainland China will be resumed by CX:

1. Hangzhou, HGH. The new weekly flight will start on May 27.
HKG-HGH CX960 1215 1440 Thursday (not available to passengers for now)
HGH-HKG CX961 1555 1820 Thursday
https://cimg7.ibsrv.net/gimg/www.fly...49e80a078f.jpg

2. Fuzhou, FOC. The new weekly flight will start on May 29.
HKG-FOC CX990 1750 1935 Saturday
FOC-HKG CX991 2045 2230 Saturday

Excellent news on the resumption of HGH and FOC flights! Do you know when they will be open for booking on CX.com? I haven't seen them yet.