generally generating debt is needed when you have unpredicted and urgent need for money (like war) and empty treasure, so limiting debt to the sum of already owned money is silly... please also have in mind that:
- council's terms are 2 months
- bills are repaid after 1 month
- you can generate so much debt that the repayment will take months or even years
- there is no information on who is using the bills to get refund and you cannot avoid repayment in any way
so there are three major problems:
a) bills are not the problem of the council that is issuing them, but the next and maybe many more upcoming councils
b) bills can be used for harassment, when the previous council is meanly creating them to keep the treasury empty and you cannot avoid repayment (you don't even know who is using the "fake" bills to put one in jail)
c) bills can be used as a weapon, when an enemy captures a castle, produces bills and even after loosing can successfuly ruin the duchy economy
in fact, there is no real need for debt more then, let's say, upkeep of an army for a month, and that's dozens of thousands, not hundreds... in my opinion the limit should be like, for example, 50% of weekly average income of county * 24 weeks (3 next councils will have to deal with 50% of income, so it's still a high limit!), there is hardly ever a real need to go beyond that