But Forbes said Houghton has not been able to contact numerous investors who were Forsyth Barr clients because their investments in the Feltex float were first registered in the name of their nominee company, Forbar Custodians Limited.
As a result Houghton has not been able to offer these claimants representation.
However, Forbes said Houghton's solicitors have been advised by lawyers for Forsyth Barr that it is intending to opt in any Forbar Custodian managed clients who invested in the Feltex initial public offering in June 2004.
"Because Forsyth Barr's nominee company is the trustee and the shares were bought in its name, they're the party that has to opt them all in, with the option being given that if they didn't want to stay in they could opt-out," Forbes said.
Forsyth Barr is one of the defendants in the litigation.
The others, who have denied the claims against them, include former chairman Tim Saunders, former chief executive Sam Magill and former directors John Feeney, Craig Horrocks, Peter Hunter, Peter Thomas and Joan Withers. Former director John Hagen is not involved in these proceedings.
Also targeted in the proceedings is Credit Suisse First Boston Asian Merchant Partners (which offered Feltex for sale), Credit Suisse Private Equity and First New Zealand Capital.
While the cut-off date for opting-in is this Thursday, some investors may also be unable to take part in the litigation if an appeal to the Supreme Court succeeds.
Last month the Credit Suisse respondents were given leave to appeal to the Supreme Court on whether some or all of the shareholders represented by Houghton were time-barred from the proceedings.