Well, if you're going to qualify your expertise in such a manner, I'll have to state that my family is from Hong Kong as well.
Let's preface this by noting that the term "soles," outside of Europe, is often improperly used to refer to many families of flatfishes outside of the
true soles of the family Soleidae.
With this in mind, we should take a look at all the fish referred to as sole available in the South China Sea.
That leaves us with 4 fishes:
Brachirus orientalis
http://fishbase.org/Summary/SpeciesSummary.php?id=8312
Cynoglossus arel
http://fishbase.org/Summary/SpeciesSummary.php?id=7523
Cynoglossus trulla
http://fishbase.org/Summary/SpeciesSummary.php?id=9243
Zebrias zebra
http://fishbase.org/Summary/SpeciesSummary.php?id=8999
Flounders native to the South China Sea include:
Pseudorhombus javanicus
http://fishbase.org/Summary/SpeciesSummary.php?id=1335
If you still haven't found your fish. I submit to you this database:
Flounders of the World
http://fishbase.org/ComNames/CommonName ... e=flounder
Soles of the World
http://fishbase.org/ComNames/CommonName ... nName=sole
I suspect, that the Chinese use of the name long li, is probably utilized in a generalized manner of referring to various types of flatfishes - whichever is currently available for sale that particular year as previous types have been overfished.
I'm sure what people were initially eating as "long li" in Hong Kong 20 years ago, is probably not what they're eating now. Since Hong Kong is a large importer of fish, particularly live species, I highly doubt that what they're eating as "long li" is even local.
In any case, I am very sure, that if one was to order long li at a Chinese restaurant, you would invariably get some type of flatfish... and hopefully not this: