gem - the cord can break / seperate from the placenta for many reasons, often due to a heavy handed doctor being a bit quick to try to pull it out, but it can happen if the cord is thin or friable (tears easily) or it is attached to membrane. There are lots of reasons and it almost certainly wont be documented in the notes. It will just say 'cord snapped'
If they did a ventouse and then changed to forceps, it was because baby would not come out with the ventouse, possibly because of lots of caput,(the swelling on babys head which doesnt let the ventouse cup attach well) or because they needed to use more traction, or force.
If they were thinking of transfusing you, your haemoglobin must have dropped quite a bit, (it normally is lower just after delivery due to haemodilution as they will have poured fluids into you, when the fluids have been absorbed the hb is higher - thats why its not accurate until at least 6 hours after birth.) so you have lost enough blood for them to classify you as a PPH.
So, the consultant will say 'difficult delivery, manual removal and PPH' and will probably suggest consultant care. You can see the interventions and complications snowballing!
However, with a second baby you will most likely have a much quicker birth, are really unlikely to need an instrumental delivery, which will reduce your chances of a retained placenta and therefore you are less likely to bleed and have a PPH.
Even less likely if you avoid an epidural and stay mobile.
I think you may have to fight to stay low risk (at least in the hospitals view) however you can also see that you will probably have a much better experience next time round, even with cons care.
Good luck and sorry for the long post and technical stuff