Deepsea,
You have to check with them. It depends on whether they still need pilots at the point of time or if there's an intake. They can't wait for you forever as there are hundreds of new applicants everytime.
Actually,
The first interview, they judge you on your personality and character. See if you really have the interest or not. HP people are very experienced in this so don't bluff your way through. Those that gets rejected here, changes can still be made as everyone changes everyday, be it mindset, goals, and etc. So you still can apply and get a few more chances.
The second call back, it means they have already accepted you for who you are and see that you are deemed fit in personality and character wise to be a pilot. You will have to go through the tests both psychometric and psychomotor. These are aptitude tests. Then it's the group project which tests you on your work communication skills. The final interview will be a grilling, to see if you can handle pressure and your knowledge. The tea party wraps everything up when they test you on your social skills. That's why it's an all-rounded thing. Those who get rejected here means that you do not have the qualities that they need. All these qualities start from young and some are inborn. You can't do much to change it. Therefore, a second chance may be very slim. But yet there are some which fail the second interview and still manage to get accepted after another try. This is due to maybe failing the knowledge test (final interview), tea party (social interaction) or the group project (work communication) by a small margin. Those can be brushed up.
The medical checkup is mainly for CAAS requirement. But SIA do have it's own requirements. For example, if you go for lasik and have 6/6 vision, still doesn't mean that you are deemed fit. They do need to check your degree before the operation and judge from there. If you fail that, means you can forget it.
there are many hurdles to cross. This is an interview, not a marriage. Know when to bull**** and when not to. Even the HR knows that. But they just want to see how you handle yourself in situations with your answers. Someone mentioned that a batch 90% of them are in for the money, and yes that's true, majority are. But my guess is they got through it all because they knew how to handle the interview. Being prepared is important.