"This has been the most successful swimming era since the mid-1990s. We won five world championship medals [all to freestyler Boyle] and two junior world championships medals [last year to backstrokers Gabrielle Fa'amausili and Bobby Gichard].
"In the aftermath to London we had eight top-50 athletes, of whom four were seen as Rio targets. Post-Rio we've got 16 in the top-50 of whom 12 look capable of going to Tokyo."
Swimming went through upheaval in the London Olympic cycle, culminating in the Moller Report of May 2012, which made 17 recommendations for change. Cotterill said the rebuild continues.
"I think we've got the right coaching in place and a new facility [at the Millennium Institute]."
He said $900,000 a year "is still a lot of money, but that investment is needed because pools and facilities are expensive to run. We can't do our training in parks or on the roads.
"The reality is the funding decision is made, but what we would like to understand is 'why?' and 'what do we need to do to get back in the good books?'."
HPSNZ chief executive Alex Baumann has kept a close eye on Swimming NZ's recent developments. As the 200m and 400m individual medley champion in world record times at the 1984 Los Angeles Olympics, he is well-placed to offer an opinion on their progress.
"They haven't had a medal since 1996," Baumann said. "There are potential athletes, but they have some way to go. We're looking at the next two years to see if they can make progress. The focus has to be on the national training centres to create the right environment for athletes to succeed."
New head coach Jerry Olszewski arrived in September from the American club scene. He said swimming's global nature, with more than 170 countries competing in Rio, had to be put into better context.
"It seems that the general public in New Zealand only measure success in Olympic sports by the colour of medals. Swimming is perhaps the hardest of all Olympic sports in which a New Zealander can succeed.
"There are no other Olympic sports with [swimming's] depth and breadth of talent, so we understand what a top-16 and a top-8 performance means."