Even though people say that whilst you still have hair or no visible thinning to anyone but yourself, then you have caught male pattern baldness in the early stages.
But by the time you notice your thinning/balding I would classify you/anyone in the advanced stages of the process. By the time other people notice your thinning/balding I would classify you in the "you are fcuked" stage.
To stop, or reverse that damage can take a great length of time for some people considering the severity of follicular damage that has occurred, hence the time frame associated for Propecia to work - if at all.
Remember that whilst you treat your loss with Propecia, damage is still occurring which is likely why it loses its effectiveness.
Therefore I can not stress enough pursuing other pathways in addition to DHT and the use of a good anti oxidative regime to prolong body clock from aging prematurely.