That is because the property transactions could be dated before the new regime came into effect.
"For several months following the law change, high numbers of buyers and sellers have not had to provide the new information as their sale and purchase agreement was dated before the law change came into force, that is before October 1, 2015. Because of this, we have gathered information for a six-month period. This gives us a larger sample size," Upston's spokesperson said.
Data from Inland Revenue indicated about 300 people a month are being issued with tax numbers for the purpose of buying or selling property here.
The October law change was aimed at tightening up the regime for foreigners buying residential properties in New Zealand.
Overseas non-resident buyers must now provide their IRD number and also have a New Zealand bank account.
A new "bright-line" test has also been introduced so that property owners must now pay tax on capital gains earned on a property which is sold within two years of purchase, although family homes are excluded.
Inland Revenue data showed that in the three months to January 31, it issued 1025 IRD numbers to foreigners who applied when they wanted to buy or sell a property here.