Originally Posted by
ISTFlyer
No, the seats are not pre-allocated by the system if the passenger doesn't choose any seat. TK does not have such algorithm as well as unless someone checks-in online and proceeds with it, no seat would be attached to a passenger.
Some seats would be automatically blocked due to operational reasons or a passenger might have previously paid for those seats.
In your case, it's very likely that Premium Economy seats were either pre-purchased by other customers ( as a datapoint Elite & Elite Plus members can't get those for free online ) or was blocked due to operational reasons such as weight-fuel balancing, VIP passengers, etc...
I serously doubt that high % of blocked seats after T-48 and before T-24 (and not exactly from T-48 from what I can see) represents seats blocked for operational reasons. Neither these look like the seats urgently purchased after T-48 by the pax in a hurry
SIN-IST flights are full now and this reflects in the number of blocked seats (compared to BKK-IST which goes slightly lighter).
And going back to SGN-IST: the flight on the 2 NOV got 'PE section' blocked too this time except the first row in the middle after T-48 (but somewhat later to be strict, maybe from T-36 or so). Interesting to know what stands behind those blockings and what is the actual TK system status of those seats showing blocked on Expertflyer.