The NPA has won control over Vancouver city council only once in the 21st century. And that occurred because of a rare combination of factors that helped the centre-right party win one of the closest civic elections in modern Vancouver history.

In 2005 there were 20 candidates for mayor, including Jim Green with Vision Vancouver and an independent named James Green.

For council, 36 candidates were vying for 10 seats. Five were with Vision Vancouver and five were with the Coalition of Electors.

The Greens fielded harm-reduction activist Ann Livingston and sustainable-transportation advocate Bev Ballantyne.

On election night, the NPA's Sam Sullivan beat Jim Green by 3,747 votes. That was less than the 4,273 votes collected by James Green.

The fourth-place finisher, high-profile environmentalist Ben West, received 1,907 votes.

On the same night, five NPA council candidates were elected, giving Sullivan's team a bare majority. Four Vision Vancouver candidates (George Chow, Heather Deal, Raymond Louie, and Tim Stevenson) and one COPE incumbent (David Cadman) also made it onto council.

Many thousands of Vision Vancouver supporters refused to vote for COPE incumbents Fred Bass, Tim Louis, Ellen Woodsworth, and Anne Roberts.

Bass ended up 2,196 votes behind Deal, who was the lowest-ranking Vision candidate.

Louis, Woodsworth, and Roberts were all more than 7,000 votes behind Deal.

The labour-backed COPE and Vision forces could have captured control of city hall and Jim Green might have won the election had there not been such enmity between these two camps.

Vision showed how to win by plumping

Roberts, now running for council with COPE, learned a hard lesson about "plumping" in the 2005 election.

In an article on Straight.com in 2014, she defined this practice as casting a small number of votes for council rather than using up all 10 votes allowed under the at-large system.

"The advantage is that you focus your voting power on the ones you really want to win," Roberts wrote. "At the same time, you don’t dilute the power of that vote by voting for someone who could end up beating your preferred candidates."

There's a great temptation for hardcore supporters of COPE, the Greens, OneCity Vancouver, and Vision Vancouver to plump in the October 20 election.

That's because these parties are running 14 candidates for only 10 spots.

Parties with short council slates are naturally going to want to concentrate their vote around their preferred candidates.

Make no mistake: Vision Vancouver's Tanya Paz and Heather Deal are chasing the same environmentally inclined voters who may want to vote for the four Green candidates and OneCity's very green Christine Boyle.

In a similar vein, OneCity's Brandon Yan is hoping to make inroads with LGBT voters who've been extremely supportive of Vision Vancouver in recent elections.

The Greens' David Wong or Michael Wiebe could conceivably find themselves in a neck-and-neck race for the ninth or 10th council spots against Vision Vancouver's Wei Qiao Zhang or COPE's Derrick O'Keefe.

These parties are frenemies. They're somewhat friendly on the surface and usually fairly civil to one another in public. But when you dig more deeply, they're also extremely competitive and antagonistic toward one another.

In this election, the NPA is running eight candidates for council.

If its traditional supporters mostly vote for the slate, they will all likely receive at least 35,000 votes and possibly more than 40,000 each.

If progressives plump, like the Vision supporters did in 2005, this will reduce the overall count of votes for non-NPA council candidates.

It's really the NPA's only hope of winning control of the Vancouver civic government.

That's because real-estate developments have added many thousands of additional voters in areas that traditionally do not vote NPA, like downtown Vancouver.

Far more votes have been cast in recent elections from East Side neighbourhoods like Grandview-Woodland, which helped Mayor Gregor Robertson win three consecutive elections.

Since 2005, areas with a large number of multifamily developments have tended to support Vision Vancouver and not the NPA.

The sprawling single-family zones on the southwest and southeast side of the city, on the other hand, have been more likely lean toward the NPA.

However, they are increasingly populated by landed immigrants, who can't vote.

That's created a structural disadvantage for the NPA.

Based on that factor alone, it's highly unlikely that the NPA will take control of city council.

The NPA faces another problem: some of its traditional supporters have launched competing parties called Yes Vancouver and Coalition Vancouver.

In light of this, the public should expect a progressive landslide on October 20.

If this doesn't happen, expect the political commentators—and some candidates—to draw upon the lessons of 2005 when they try to explain what happened.

Plumping can offer advantages for individual parties in a close election.

Yet when it happens on a large scale among supporters of progressive parties running short slates for council, the largest beneficiary can conceivably be the NPA.