Now, here is what is the source of info:
1- Whenever I travel by trains, I make it a point to check the reservation charts pasted on trains (not just my train, but also train stopping on opposite platform). It gives you a good idea as to how quotas are organized in trains.
2- There was a website hosted by IR railways (irsuggestions.org) in which even the railway officials used to participate. They have themselves given this information.
3- I...
more... am a member of IRFCA.
4- I also keep on querying the reservation website, to get more information.
5- Plenty of PNRs on this website prove that this quota spans across starting station of the train till ending station.
And the reason that I am writing here is not to convince you, that’s not my intention. There are thousand other users of this blog site who need information, and I want to make sure that they don’t get it wrongly. It is for their benefit that I am explaining the reservation system of Indian Railways. Note that you find documentation of this anywhere in any website or books of Indian Railways.
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So finally, PQ is end to end quota, defined to restrict some source-destination combinations to only this quota, thereby benefiting the end to end travelers. It is configured differently in different trains. For more info on PQ, refer blog number 28909.