Regards to RECOMMENDED FOR COMBINATION BY AB I coincidentally today read the IUCN ev of Trang An. It even hints to 2 combinations:
1. With the South China Karst (but "Given there is already an ongoing process of extension of the South China Karst World Heritage Site in China, it
appears to be difficult to insist on Trang An being directly connected to that process")
2. With Ha Long Bay ("What appears to be more appropriate to recommend is that Viet Nam might consider a parallel process to the
Chinese South China Karst nomination, where a number of key karst sites have been nominated as part of a
coordinated process, in a national serial approach. Noting that a key comparison for Trang An is the site of Ha Long Bay, the relationships to Ha Long Bay and the adjoining Cat Ba Archipelago would seem to warrant further consideration, notwithstanding the challenges of Trang An being nominated as a mixed site."

Is this enough of a "recommendation"?

Yes - I think that "knowledge" of and easy reference in future to, this "adds value" for all of us - and that, after all is why we have "Connections"!
Perhaps the text could indicate that its was a "proposal for consideration" rather than a "recommendation" by the WHC - we could use text to indicate the "strength" of the "recommendation" for combination.

Do we have a connection for "unofficial passport stamp available"? ie. Machu picchu, galapagos and easter island. Maybe there are more, my brain is still in south america though...

Every place in Korea has a stamp, you could even get a booklet in 2016 or all of them. I collected all but didn't get a souvenir.

https://english.visitkorea.or.kr/enu/CU/CU_EN_8_5_9_1_1.jsp

Some places have different stamps and the Dolmen sites in the south were little tricky to ask for the "correct" one.

We could find a great many! The US also has a booklet to receive stamps for all 23 of its WHS.
Then of course the Santiago de Compostela route has its own "passport" - which will cover a fair number of other WHS!
Apparently the Tourist office in San Marino will stamp your passport for 5 Euro with a San Marino "country" stamp - would that "count" as a "WHS" stamp for this Connection if we were to have it?

Reading about this niche "travel hobby" it appears that people actually try to get "unofficial" stamps put into their REAL passport!!!! I have spent my travel career trying to avoid having even "official" ones put in mine!! And one of my travel "bêtes noires" is the unthinking border official who unnecessarily starts a new page!!!

Yeah I got one from San Marino and Lichtenstein, but those are grey area as they are from a country and not the East Berlin scam going on at Checkpoint Charlie. Sure they come from the "tourist office" but still. I stamped both into the Observation section.

Interesting
From your continuing (unhindered?) travels to a wide range of countries it can presumably be assumed that it hasn't caused you any problems at "immigration" but - I would have thought that the "Observation" section (Called "Endorsement section" by US) was potentially the more "significant" one in a passport compared with the "Visa" pages.
On a UK passport it states "This page is reserved for official observations". Many of these are of a standard content and format.
"The Observations page is for authorised immigration officials to make notes (observations) that may be useful for other immigration officials to know later. These could include "Deported xx-xx-xxxx for yyyyy reason, zzzzz country" or "Overstayed xx days yyyy country, barred re-entry yyyy until zz-zz-zzzz" Things which would influence entry decisions and which should be seen quickly without flipping through and checking entry/exit dates on every page."!!!!

True but I should show you examples of mistakes the immigration officers have made around the world like wrong stamps and then crossed out and no way I have proof that it was me or the officer, or stamping over other stamps, I'm not worried. I even had official stamps on the observation page if the officer is in a rush. I only had one problem ever and it was EXITing a country: Israel, and I don't want to talk about the details (they seem to have a brief interview with everyone though).

I should mention that I regularly apply a new passport to avoid these things and don't wait until it gets full. Traveling to the Middle East is an instant excuse to get a new one issued thanks to our big brothers in the south and their paranoia. I have of course entered with a stamp from the UAE before but it meant asking me a single question "what were you doing in the Middle East?" and that's all.

We just had a similar experience entering the US. The official looked at our Moroccan stamps and asked us "What were you doing in Palestine?"
The stamp does have FEZ written in Latin Script on it, but I guess decent geographic wasn't a prerequisite for boarder officials.

I guess I was originally thinking of the stamps that go in passports but I had heard of these booklets of stamps for pilgrimage trails too. I never had a problem with the few I've put in my passport over the years for places like Lichtenstein and Timbuktu (oh, I guess that is another one for the list) but I generally decline now. I fill up my passports too fast anyway. Couldn't say no to a few from Antarctica on this trip though it is going to get very tight getting home with the space I have left. Will probably have to see if I can convince someone to use the observation section...

There were 2 recent reports in my country that immigrations in Taiwan and Singapore denied entry because those passports had souvenir stamps from Japanese temples and amusement park, Hello Kitty stamp and seal stamp. In my experience I did have souvenir stamps in my passport, San Marino, Liechtenstein, Machu Picchu, Easter Island's Moai, Bat stamp from Mammoth Caves etc. including the red stamp of Tax-refund shopping in Japan and went to Taiwan and numerous to Singapore, and did not have any problem. Maybe those souvenir stamps were issued by municipal or state agencies, so immigration officer possibly OK with these (?) but better to avoid those stamps with cartoon or mascot.

Well that's just silly.

How about "cash only ticket"? I know there are great many but still very surprised that Europe has some. Villa d'Este is now a whopping €13 cash only, plus €4 for the audio guide. Another surprise was in Weimar but I can't say all of them are cash only.

I find the connection "Lynx" a little odd seeing that they could potentially be found in many park in North America from the Canadian Rockies to Yellowstone to the Everglades. Sure you want such a broad connection?

I wondered about that as well when the connection was first posted. My thought at the time was that the connection probably meant "Eurasian Lynx" as opposed to the other three species from the genus Lynx, but I can't say for sure. Perhaps this can be clarified?

All (4) species of Lynxes are considered I guess. The Iberian Lynx is the only one that is really rare. I don't know how common it is to see a (Canadian) lynx in Canada. I have never seen one.

We have connections for Penguins as well for example, these are quite common and fairly wide-spread around the world .