This is a shot in the dark.

Actualiser means to update as well as to discount. I suspect the writer thinks (or is assuming) that when a figure is updated it's always increased, so he feels he can't use it when the figure is DEcreased. He therefore invents a verb to mean to update by decreasing.

What else? To "de-update" isn't a concept I'd care to explore, and according to a usually reliable site, désactualiser doesn't figure in any French dictionaries.

You could always ask the client for an explanation. I do that all the time. We needn't pretend to be omniscient!

no idea if it is the same, but you can always double check

As in "the discount on the provision is progressively unwound" - or possibly 'the provision is progressively unwound".

I have never come across "accreted" or "accretion" in this context, but first came across "unwinding" for "désactualisation" from corrections made to one of my translations by a UK accountant - maybe it's a British-specific term and "accretion" is used more across the Atlantic?

I have also seen "reverse discounting", but as I Googled for examples I noted that all the examples found were in translations from the French.

Hey! I've just found an example with both "accretion" AND "unwinding the discount", from one of the major accountancy firms:
The amount of accretion in the provision from unwinding of the discount gives rise to a book/tax difference and will result in a deferred tax asset, subject to an assessment of recoverability.
http://www.pwc.com/extweb/service.nsf/docid/020EF90FE9632A5E...

Some "unwinding" examples from British sources, the first two using "unwinding the provision" directly without mentioning the discount:

Calculate the discounted provision and demonstrate how the provision is unwound over following years (exam question)
http://64.233.183.104/search?q=cache:uB0thkOAoQkJ:www.cipfa....

Elsewhere on expenditure, as a consequence of the special cumulative adjustment necessary in 2005-06 to meet HM
Treasury’s advised reduction in the discount rate to be used for the unwinding of provisions from 3.5 to 2.2%, a significant
increase was required to the Council’s cumulative charge which cost £5.9 million in 2005-06. This year, no such adjustment
has been advised and therefore the charge to expenditure required this year was reduced to £0.8 million.
http://www.scitech.ac.uk/images/CCLRCAR0607.pdf

As stated in Note 1.15 the requirement of Financial Reporting
Standard 12 has been adopted to state the early release and
pension commitment provision at a discounted amount where the
time value of money is material. The provision for the estimated
payments has been discounted by the HM Treasury discount
rate of 2.2% in real terms. The discount is unwound over the
anticipated duration of the provision.
http://www.ordnancesurvey.co.uk/oswebsite/aboutus/reports/an...

The income statement charge is split between an operating charge and a net finance charge. The net finance charge relates to the unwinding of the discount applied to the liabilities of the scheme offset by the expected return on the assets of the scheme, based on conditions prevailing at the start of the year.
http://www.btplc.com/report/Report05/Financialreview/interna...


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Note added at 22 hrs (2008-06-11 07:19:35 GMT)
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Thanks rkillings for the clarification. I didn't mean to suggest that accretion wasn't used, we all know that not having come across a term before is proof of nothing! As you can tell, désactualisation is not a term I encounter much and you didn't mention IAS/IFRS in your initial answer - plus, although I searched before posting an alternative answer, even accretion + IFRS didn't come up with anything to suggest that unwinding was wrong. But as usual I suppose the IFRS term will take over. Would you say "unwinding" is out of date or just a British English term? Anyway, je me coucherai moins bête ce soir!