Several years after negotiable bonds secured by a mortgage of benefit assessments had been issued by a municipal improvement district  statutes were passed which greatly diminished the remedies for their security provided by law at the time of their issuance  viz: the time within which an assessment might be foreclosed and the assessed land sold for default in payment of the assessment was enlarged from approximately 65 days to at least 2 1/ years  and it might be much longer  provisions for adding a penalty of 20%  as well as costs and attorneys' fees  were altered by omitting the costs and attorneys' fees and reducing the penalty to 3%  a provision allowing the purchaser at foreclosure sale to go into possession upon confirmation of the sale and keep the rents and profits during the years allowed for redemption was repealed  so that the possession of the delinquent owner might remain for another four years unaffected by the sale