Discontinued tickers

Hi,

I have a question about discontinued tickers, namely following:

'CZFCS04' : ECBOT - 5 YEAR US T-NOTE CONT.INDX

'CZNCS04' : ECBOT - 10 YEAR US T-NOTE CONT.INDX

'CZUCS04' : CBOT - LONG TERM ULTRA ELEC. CONT.INDEX

'ATDCS04': SFE - AU 3 YR T-BOND DAY CONT.IDX

Any reason why they are discontinued (all in this year). I was under the impression that these are continuous tickers and would be updated daily. If possible, I would also like to know what alternative tickers could be used instead of these as a continuation to discontinued time series.

Thanks