On the ex-date CREST credits a nil-paid rights ISIN against the cum holding. That line usually lives for about two to three weeks, matching the acceptance window. Take-up is an instruction plus cash; the nil-paid is cancelled and fully-paid ordinary stock is credited. Until that happens the holder owns a right, not the new share, and the two ISINs must not be collapsed in the position file.
To let the right lapse in CREST, the participant sends an ACON. Without it, market practice on an unsettled bargain is that the seller takes up for the buyer: the seller pays the call so the buyer is not left unhedged when the nil-paid dies. That default is in the London rulebook, not a courtesy. Missing the ACON is how a seller accidentally funds a buyer's take-up.
Buyer-protection deadlines sit earlier than the market deadline. A late client election does not make the broker the insurer of a missed agent cut-off. Firms work on reasonable endeavours: they will try to get a late instruction through; they will not guarantee the registrar's clock. The control is an earlier client cut-off, not a promise to backstop a miss.
Atlantic Horizon UCITS ICAV's Thames Industrial plc line is the CREST case. Ex-date, State Street sees a new nil-paid ISIN credited against the 400,000 ordinary. Dublin has to show both lines before dealing: 400,000 fully paid, 100,000 nil-paid on a 1-for-4. The manager's take-up MT565 has to reach State Street before the agent cut-off, with £200,000 of ICAV cash dual-controlled. No message, and no ACON on an open bargain, and the default fires.
Irish UCITS administration cannot outsource the last NAV stamp or the shareholder register while that nil-paid line is live. State Street can be right in CREST and Dublin still wrong in the fund books. Incoming dealers on the ICAV are buying a price that either includes the right or does not. The Cayman sleeve uses the same custodian clock; it does not get a second CREST participant for the same ISIN.
Nippon Industrials KK (Tokyo, ISIN JP3899200005) will not follow this spine. A Japanese allotment to existing holders typically has no CREST nil-paid, no ACON, and no London seller-take-up default. The Japanese sub-custodian credits an entitlement, waits for cash, and either delivers new shares or lets the offer die. Copying a CREST ACON onto Tokyo is a message the agent cannot read.
Processing is a diary, not a single booking. Ex-date credit, dealing window, cash call, extinguishment, fully-paid credit, lapsed placing if any, then the three-way rec. Miss one day of that diary and the next day's NAV is a story about yesterday's position.