If the notary pre-dates the document it is illegal. However, there may be no evidence to prove it is illegal and probably no one would even object to it as illegal ...
I have a question, how does the Indonesian notaris notarize the document if you are overseas. Isn't he supposed to witness you signing?
As for trusting an Indonesian notaris, I wouldn't. I contacted 2 or 3 before we found one that would do it at a reasonable price (he quoted 300k) and then I emailed him what I wanted it to say. When we showed up at his office, he gave us the standard form pre-nup, which is exactly what we didn't want because it wouldn't work for our situation. I again gave him exactly what we wanted (written in English and with a translation); when we came back a few days later it was wrong again. He had added a bunch of crap from the standard form we didn't want, so I told him again what I wanted and we watched him make the changes, which he did although grumbling the whole time. It was finally done and signed and then he asked us for 1.5M because we made him change it so many times. I explained to him that had he done it right the first time it would have taken him less time than even typing up the standard form, since ours was very short. At any rate, he lost all hope of any future business from us due to his incompetence and last minute attempt to up his fees.