According to parliamentary library research given to the Green Party, Sue Moroney's bill extending paid parental leave to six months would have been passed, as would two other Labour private member's bill that were tied last week.
If Mr Peters wins, his caucus will increase from 11 to 12 with the addition of a list MP to replace him on the list.
The Opposition benches would increase by one and National would have 59, instead of the 60 it had after last's year's election in a 121 seat Parliament.
It would still have a comfortable majority to govern, 63 to 58, with the support of Act, United Future and the Maori Party on confidence and supply bills, including the Budget.
But a New Zealand First win in Northland would give Mr Peters' party and National's support parties more power on other bills.
Korea Free Trade Agreement
Legislation will need to be passed amending the Tariff Act 1988 which even New Zealand First, anti-free traders, will support. Will pass whether or not Mr Peters wins Northland with the support of Act and United Future.
But Labour is almost guaranteed to vote for it too along with NZ First.
Resource Management Act reform
A bill has yet to be introduced by Nick Smith but before the resignation of Mike Sabin, National was planning to pass its next RMA reforms with the support of just Act if need be because of objections by United Future and the Maori Party.
Mr Peters has said he would be willing to discuss reforms, although he voted for the last set of reforms National put up in 2013.
Fighting Foreign Corporate Control Bill
A private member's bill in the name of New Zealand First MP Fletcher Tabuteau, which would ban Government from signing free trade agreements with investor-state dispute procedures - a binding arbritration process to settle disputes between exporters and Governments if particular Government actions reduce the value of the business. The Korea FTA has one as does the China FTA. This bill would definitely have enough support to pass its first reading and get to select committee with a Peters win in Northland because Labour has committed to voting for its first reading.
Without a Peters win in Northland, National would vote down the bill with the support of Act and United Future.
International Convention Centre Act
A private member's bill in the name of New Zealand First deputy leader Tracey Martin which repeals the law establishing concessions to Sky City for building the New Zealand Convention Centre. National just has the numbers to vote down the bill with the support of United Future and Act, which initially waivered on whether it would support it or not. An approach from Economic Development Minister Steven Joyce to Act leader David Seymour was persuasive.
Parental Leave and Employment Protection(Six Months' Paid Leave) Amendment Bill
Private member's bill of Sue Moroney which extended paid parental leave to six months. Was discharged in February after a tied vote and the support of NZ First. With a Peters win in Northland, it would have had the numbers to pass - although National would have exercised a financial veto which it can do when private member's bills or amendments cost money.
Education (Food in Schools Bill)
A private member's bill in the name of Labour MP David Shearer which would have provided free food in all decile one to three primary schools and intermediates that wanted it. It was tied 60 all so failed to pass its first reading. NZ First supported it and with one more MP it would have gone to select committee for consideration.
Healthy Homes Guarantee Bill
A private member's bill in the name of Labour MP Phil Twyford, it provided for minimum standards of heating and insulation in rental accommodation. It had the support of NZ First but was tied 60 all so did not pass its first reading. A Peters win in Northland, with the extra list MP that would bring would have seen the bill proceed to select committee.
