Seagull S6 Truss Rod Adjustment Location

[Raydarnsky]

I have seen Seagull S6's with the truss rod adjustment cover on the head under a cover and also S6's without the cover which I assume is the newer design truss rod adjustment through the sound hole. Can anyone put a date on when this change was made and is either one better? Thanks in advance for the vast knowledge base on "Acoustic Guitar Forum"