The Department of Finance explains the data revision here. In terms of the GGB in 2010 and subsequent years, there is an interesting set of communication issues. As per the DF note, one approach is to make a sharp distinction between the ‘headline’ and ‘underlying’ GGB with the difference consisting of the ‘unrequited’ capital transfers into Anglo-Irish etc. (as opposed to the equity-type investments in AIB and Bank of Ireland). This distinction may be effective if the bank-related capital transfers are a ‘once off’ event or a “twice off” event (ie 2009 and 2010) but may lose its force in relation to a steady sequence of capital transfers over the next decade. To the extent that the promissory notes spread out the capital transfers over a long period, this may be a downside to this approach relative to making a larger-but-final capital transfer in 2010.
Update/clarification: The promissory note approach will not affect the timing of when capital transfers hit the GGB (once the capital transfer is decided, it hits the GGB in that year in line with accruals accounting) or when the fiscal cost of bank re-capitalisation hits the gross government debt (again, it hits the gross debt at the time of the commitment, since the liability has been accrued). Moreover, the impact on the gross debt happens immediately even if it takes time (as in the 2009 case) to determine whether the re-capitalisation is an equity-type investment or a capital transfer. The promissory note approach just spreads out the timing of the cash payments.