Cervello's Mr Daems adds: "We are yet to see a truly accurate picture of how smaller businesses have adopted automatic enrolment.
"Firstly the data we have is running a few months behind the reality of the market due to the amount of time employers have to complete their declaration of compliance.
"Secondly, we have all of this year to go, as a decent number of the smaller firms, as well as newer employers, have to comply."
Then there are others outside of the workplace pension system who may need some form of legislation to bring them into an auto-enrolment style scheme.
Helen Baker, partner at law firm Sackers, adds: "There are some people who are not yet caught by the auto-enrolment net, such as the self-employed and those with multiple jobs who do not qualify for auto-enrolment in any single job.
"These groups are a particular focus for the government in its current review."
There have been several measures over the intervening years to help employers/scheme sponsors, advisers, employees, pension providers and administrators to make it easier to help get more people into a workplace pension.
Initially, small to medium-sized employers (SMEs) had until 2015 to prepare; this was extended to ease the burden on Britain's smallest businesses.
Subsequent legislation has aimed to help the smallest and micro-employers, as well as new employers who have recently come into existence, set up auto-enrolment processes.
This is necessary - but more is still needed to iron out some concerns, as Andy Agathangelou, founding chairman of the Transparency Task Force, explains.
"There are areas of concern, such as the fact the employer burden for the smallest and micro employers is disproportionate", he says.
"Error rates on their declarations of compliance are worryingly high, with some research indicating 26 per cent are likely to result in member detriment.
"Moreover, hearts and minds of employers and workers have not been won, so we may have highly precarious opt-out rate resilience, especially when contribution rates rise", Mr Agathangelou adds.
Adrian Boulding, retirement director of the Tax-Incentivised Savings Association, comments: "Auto-enrolment has been a great success to date.
"The 2017 review will help the financial services industry to identify ways of building on that success.
"It is widely acknowledged that contribution levels need to rise, so initially we need to ensure the increases in 2018 and 2019 are implemented as planned."
He adds: "As we go through this period of transition and look to establish an auto-enrolment solution that delivers realistic and relevant outcomes, engagement will be at its heart.