Thailand - 1947 King Definitives

Going through my small Thailand collection today for the first time ever. Noticed this group of King definitives from 1947-1949 (Scott #264-273). Since they were in nice shape & complete set checked the value. Was very surprised to find the mint high value ones/complete set going for hundreds of dollars on ebay.

Does anyone have background as to why these are so valued? I did a search but couldn't find any info on them, beyond their price... On the face of it, they are semi-modern definitives, not what you'd expect to be higher value.

Thanks! ~gmot

No idea,
I have been out-bid every time trying to secure these.
Yours look in tip top shape. Very nice.

Thanks Rod - very lightly hinged but in great condition. Hiding in an album for 70 years has kept them fresh :)