Should triplets be marked only on the first bar?

[citizen_k]

Hi Guys, a simple theory question:
I came across Debussy's Arabesque #1  which contains 8th triplets on the first several bars, but the triplets are marked only on the first bar.
(Excrepted image attached)
Is there any notation rule that allow indicating triplets only on the first bar, while the player has to guess about the following bars?

Many thanks!

[perfect_pitch]

If the piece is heavy on triplets, it's assumed that as a piano player that if you see groups of 3 quavers in simple time, that they will be triplets and not standard quavers.

Probably just saves the editor and transcriber a little time and effort.

[citizen_k]

Thanks. makes sense.
I was confused because later on in the score the triplets are gone and notes become 8xEights, so who is not familiar with the piece needs to put a lot attention to the metre.