It seemed like we'd finally got the hang of picking those tired signs and getting DS down at the right time, when it all stopped working. From around 6 -8 months we struggled on till I finally gave up. Things got better when I realised that DS would NOT go to sleep when he was tired. Oh no. He had to be absolutely shattered. Only then would he acquiesce.
So I ignore the tired signs (hell, he's tired pretty much all the time) and wait for the stumbling, falling over drunk-like exhausted signs.