well for certain sectors they give 40+7 but u need to read the rules of your ticket carefully.

if the ticket is purchased from Doha and if you r flying out of doha to non GCC countries you are allowed different baggage allowances

23kg baggage allowance for all economy passengers travelling on QR flights.

But,

 TOTAL BAGGAGE ALLOWANCE ALLOWED FOR  KTM  IS
   2 PIECES 35 KG TOTALFOR ECONOMY CLASS ON
   OUTBOUND  ONLY.
   --------------------------------------------------
   TOTAL BAGGAGE ALLOWANCE ALLOWED FOR AMD / COK /
   HYD /KHI /MAA /TRV/BLR IS  2 PIECES 40 KG TOTAL
   FOR ECONOMY CLASS AND 50 KG  FOR BUSINESS CLASS
   ON OUTBOUND ONLY.
   -------------------------------------------------
   TOTAL BAGGAGE ALLOWANCE ALLOWED FOR BOM / CMB /
   DAC / DEL / ISB / LHE / PEW  IS  40 KG FOR ECONOMY
   CLASS AND 50 KG  FOR BUSINESS CLASS ON OUTBOUND
   ONLY.

I hope you are familiar with the 3 letter codes of the cities.

So you see it differs and I do agree with you if you say that the original Ticket said 40Kgs even if its a printing error, it is document proof!!!

You can fight for your rights.

All the best!!!