More phone lines should have been used ahead of the general election in Northern Ireland, the chief electoral officer said.
The Electoral Office received an "unprecedented" 13,775 applications to vote on the deadline for registration last November.
It has faced criticism in some quarters over how the election was conducted amid claims people had been denied a vote in the December 12 poll.
Chief electoral officer Virginia McVea said: "The most telling piece of data perhaps of all is that 46% of all those applications for the parliamentary election were received in the last six days.
"This compares to 15% of all applications in the last six days of the local election which totalled 7,199 compared to over 40,000.
"This huge rush at the end was unprecedented for Northern Ireland."
After every election she said the organisation reviewed all polling station logs to learn lessons.
Ms McVea said: "The first phase of this is complete and the only systemic issues emerging were that more phone lines would help and a request to make the Register easier to read."
The office received under 200 complaints, fewer than at previous elections. This is for an eligible electorate of around 1.3 million.
The Electoral Office has been waiting to set up a new telephone system for some time.
Ms McVea said: "The number of unplanned elections in the last three years interrupted this work but now that we believe we have a period between elections which will enable us to do the work on the phone system we are currently awaiting contractors who will as part of their work put more lines in to the office.
"During one day in the lead up to the election BT phone lines were down in part of Belfast. This was an issue with BT and not the Electoral Office Northern Ireland.
"We followed best advice during those hours which involved using mobile devices."
She issued a report on alleged administrative irregularities to the Northern Ireland Office.
