You are right Beadley
I finished mine and waiting for my certificate could be months away 
I think you sign up to pay a set amount and thats fair to everybody and is agreed legally
what I dont think is fair regardless of windfalls etc  is that you get the PPI being paid out or not and then you are hanging on and being put under further constraints and worrying and its not your fault
If you ask for a payment break or a lesser payment you get an immediate response saying no you cant or you have to do this and then wait etc  But when you complate as you set out to do and then are told oh well its going to be another 6 months   never mind  its just not right or fair 
At the end of the IVA regardless of what has happened you should get taht certificate in your paws  within 10 working days 
they have had 5 years to prepare they know you are paying a set amount and how much is going to be there at the end 
Even with pay increases  that can be added on at the end its not rocket science  If you pay in £20 000 for 5 years get a pay rise for the last year they just add that in 
The IVA agreement is you paying them and thats you have done  what happens after is down to them to deal with
PPI should not come into it or windfalls 
If you get lucky and win something then you can choose to pay it or not 
Basically I look at it as I was in a mess they let me pay a whole lot less back and I am glad its all over   draw a line here and now and move on 
All legal things take time and you are dealing with a large amount of admin and office workers
I actaully went to an IVA firm and saw what they do in there call centres a huge room with pcs and people wandering around with headsets and clip boards and a lot of yonng people  You would imagine a few highly trained older types and stacks of legal books piled up with a grandfather clock in the background 
So remember to factor that in when you are waiting for a response things go missing information is not always passed on  emails are deleted papers go walkabout   people go on holiday etc  so with xmas on the horizon I give up for this year