It may be the way colours show on my screen, but you seem to have a bit of toning, or tropicalisation, on some of those blocks, particularly the SG 27. My copies of SG 27 and the surcharges on it also are rather toned.
I've also noticed that SG 65 often seems to have backing paper adhering to it. The gum on that stamp must have been particularly unsuitable!
The block of SG 115s is very nice indeed, though. Gibbons prices these at £100 each mint. As they're only £1 each used, few collectors can have bothered to buy them when they were current. The commonest Travancore-
Cochin 3 Anna, SG 6a (the 3 Anna surcharge on Travancore 7 Chuckram pale blue, perf 11) is priced at £6.50, so it's easy to see what collectors were buying around 1950!
Incidentally, there's a good flaw on the
Cochin SG 115: a line from the Maharaja's mouth:

It's constant, on both the normal and Ser
vice overprints, and worth looking out for. Of course, all these 6th Raja stamps have numerous plate flaws, but this is a particularly striking one.